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 $244.88   9.534%   $268.2269   $268.23   $268.25   $268.20  
  Purchase #2 $39.65   4.156%   $41.2979   $41.30   $41.30   $41.30  
  Purchase #3 $122.95   12.548%   $138.3778   $138.38   $138.40   $138.40  
  Purchase #4 $30.88   4.293%   $32.2057   $32.21   $32.20   $32.20  
  Purchase #5 $30.82   8.732%   $33.5112   $33.51   $33.50   $33.50  
  Purchase #6 $247.27   5.422%   $260.677   $260.68   $260.70   $260.70  
  Purchase #7 $182.55   10.803%   $202.2709   $202.27   $202.25   $202.30  
  7 purchase totals = $899.00       $976.5674   $976.58   $976.60   $976.60