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 $71.61   7.176%   $76.7487   $76.75   $76.75   $76.70  
  Purchase #2 $230.69   3.172%   $238.0075   $238.01   $238.00   $238.00  
  Purchase #3 $224.57   8.468%   $243.5866   $243.59   $243.60   $243.60  
  Purchase #4 $130.56   8.518%   $141.6811   $141.68   $141.70   $141.70  
  Purchase #5 $40.74   7.189%   $43.6688   $43.67   $43.65   $43.70  
  Purchase #6 $197.25   8.454%   $213.9255   $213.93   $213.95   $213.90  
  Purchase #7 $57.92   7.548%   $62.2918   $62.29   $62.30   $62.30  
  7 purchase totals = $953.34       $1,019.9100   $1,019.92   $1,019.95   $1,019.90