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 $136.75   12.371%   $153.6673   $153.67   $153.65   $153.70  
  Purchase #2 $63.28   12.203%   $71.0021   $71.00   $71.00   $71.00  
  Purchase #3 $156.78   13.762%   $178.3561   $178.36   $178.35   $178.40  
  Purchase #4 $48.44   9.149%   $52.8718   $52.87   $52.85   $52.90  
  Purchase #5 $55.32   12.530%   $62.2516   $62.25   $62.25   $62.30  
  Purchase #6 $182.39   8.171%   $197.2931   $197.29   $197.30   $197.30  
  Purchase #7 $44.66   6.706%   $47.6549   $47.65   $47.65   $47.70  
  7 purchase totals = $687.62       $763.0969   $763.09   $763.05   $763.30