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 $64.48   12.808%   $72.7386   $72.74   $72.75   $72.70  
  Purchase #2 $35.97   5.213%   $37.8451   $37.85   $37.85   $37.80  
  Purchase #3 $103.41   12.471%   $116.3063   $116.31   $116.30   $116.30  
  Purchase #4 $68.82   5.419%   $72.5494   $72.55   $72.55   $72.50  
  Purchase #5 $162.71   9.355%   $177.9315   $177.93   $177.95   $177.90  
  Purchase #6 $248.80   4.627%   $260.312   $260.31   $260.30   $260.30  
  Purchase #7 $69.74   5.763%   $73.7591   $73.76   $73.75   $73.80  
  7 purchase totals = $753.93       $811.4420   $811.45   $811.45   $811.30