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 $217.87   12.291%   $244.6484   $244.65   $244.65   $244.60  
  Purchase #2 $235.92   7.237%   $252.9935   $252.99   $253.00   $253.00  
  Purchase #3 $124.71   8.333%   $135.1021   $135.10   $135.10   $135.10  
  Purchase #4 $246.72   3.717%   $255.8906   $255.89   $255.90   $255.90  
  Purchase #5 $152.29   9.507%   $166.7682   $166.77   $166.75   $166.80  
  Purchase #6 $127.86   7.412%   $137.337   $137.34   $137.35   $137.30  
  Purchase #7 $219.78   6.480%   $234.0217   $234.02   $234.00   $234.00  
  7 purchase totals = $1,325.15       $1,426.7615   $1,426.76   $1,426.75   $1,426.70