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 $61.69   3.594%   $63.9071   $63.91   $63.90   $63.90  
  Purchase #2 $177.82   6.296%   $189.0155   $189.02   $189.00   $189.00  
  Purchase #3 $76.94   9.765%   $84.4532   $84.45   $84.45   $84.50  
  Purchase #4 $137.52   6.417%   $146.3447   $146.34   $146.35   $146.30  
  Purchase #5 $97.89   10.520%   $108.188   $108.19   $108.20   $108.20  
  Purchase #6 $143.36   9.532%   $157.0251   $157.03   $157.05   $157.00  
  Purchase #7 $170.34   9.203%   $186.0164   $186.02   $186.00   $186.00  
  7 purchase totals = $865.56       $934.9500   $934.96   $934.95   $934.90