Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $193.71   6.442%   $206.1888   $206.19   $206.20   $206.20  
  Purchase #2 $171.74   11.215%   $191.0006   $191.00   $191.00   $191.00  
  Purchase #3 $239.89   3.704%   $248.7755   $248.78   $248.80   $248.80  
  Purchase #4 $203.45   12.833%   $229.5587   $229.56   $229.55   $229.60  
  Purchase #5 $122.27   9.364%   $133.7194   $133.72   $133.70   $133.70  
  Purchase #6 $188.31   6.124%   $199.8421   $199.84   $199.85   $199.80  
  Purchase #7 $243.57   12.407%   $273.7897   $273.79   $273.80   $273.80  
  7 purchase totals = $1,362.94       $1,482.8748   $1,482.88   $1,482.90   $1,482.90