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 $131.89   11.694%   $147.3132   $147.31   $147.30   $147.30  
  Purchase #2 $140.92   13.295%   $159.6553   $159.66   $159.65   $159.70  
  Purchase #3 $209.86   3.655%   $217.5304   $217.53   $217.55   $217.50  
  Purchase #4 $20.37   11.706%   $22.7545   $22.75   $22.75   $22.80  
  Purchase #5 $8.53   9.635%   $9.3519   $9.35   $9.35   $9.40  
  Purchase #6 $249.66   6.625%   $266.2   $266.20   $266.20   $266.20  
  Purchase #7 $180.45   6.294%   $191.8075   $191.81   $191.80   $191.80  
  7 purchase totals = $941.68       $1,014.6128   $1,014.61   $1,014.60   $1,014.70