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 $228.90   13.677%   $260.2067   $260.21   $260.20   $260.20  
  Purchase #2 $22.43   13.397%   $25.4349   $25.43   $25.45   $25.40  
  Purchase #3 $243.68   12.377%   $273.8403   $273.84   $273.85   $273.80  
  Purchase #4 $88.69   9.330%   $96.9648   $96.96   $96.95   $97.00  
  Purchase #5 $245.48   5.766%   $259.6344   $259.63   $259.65   $259.60  
  Purchase #6 $178.58   9.130%   $194.8844   $194.88   $194.90   $194.90  
  Purchase #7 $142.77   5.738%   $150.9621   $150.96   $150.95   $151.00  
  7 purchase totals = $1,150.53       $1,261.9276   $1,261.91   $1,261.95   $1,261.90