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 $62.71   9.526%   $68.6838   $68.68   $68.70   $68.70  
  Purchase #2 $191.25   12.536%   $215.2251   $215.23   $215.25   $215.20  
  Purchase #3 $53.58   9.475%   $58.6567   $58.66   $58.65   $58.70  
  Purchase #4 $220.42   3.222%   $227.5219   $227.52   $227.50   $227.50  
  Purchase #5 $42.79   13.115%   $48.4019   $48.40   $48.40   $48.40  
  Purchase #6 $136.68   5.394%   $144.0525   $144.05   $144.05   $144.10  
  Purchase #7 $189.64   11.733%   $211.8905   $211.89   $211.90   $211.90  
  7 purchase totals = $897.07       $974.4324   $974.43   $974.45   $974.50