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 $166.34   11.748%   $185.8816   $185.88   $185.90   $185.90  
  Purchase #2 $40.79   12.364%   $45.8333   $45.83   $45.85   $45.80  
  Purchase #3 $241.76   13.234%   $273.7545   $273.75   $273.75   $273.80  
  Purchase #4 $198.34   4.647%   $207.5569   $207.56   $207.55   $207.60  
  Purchase #5 $185.41   4.412%   $193.5903   $193.59   $193.60   $193.60  
  Purchase #6 $59.66   6.365%   $63.4574   $63.46   $63.45   $63.50  
  Purchase #7 $34.51   6.151%   $36.6327   $36.63   $36.65   $36.60  
  7 purchase totals = $926.81       $1,006.7067   $1,006.70   $1,006.75   $1,006.80