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 $86.44   9.571%   $94.7132   $94.71   $94.70   $94.70  
  Purchase #2 $235.94   3.728%   $244.7358   $244.74   $244.75   $244.70  
  Purchase #3 $98.45   10.515%   $108.802   $108.80   $108.80   $108.80  
  Purchase #4 $208.31   11.529%   $232.3261   $232.33   $232.35   $232.30  
  Purchase #5 $19.50   12.291%   $21.8967   $21.90   $21.90   $21.90  
  Purchase #6 $22.88   11.113%   $25.4227   $25.42   $25.40   $25.40  
  Purchase #7 $58.98   11.344%   $65.6707   $65.67   $65.65   $65.70  
  7 purchase totals = $730.50       $793.5672   $793.57   $793.55   $793.50