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 $62.30   13.201%   $70.5242   $70.52   $70.50   $70.50  
  Purchase #2 $46.96   4.265%   $48.9628   $48.96   $48.95   $49.00  
  Purchase #3 $190.45   6.228%   $202.3112   $202.31   $202.30   $202.30  
  Purchase #4 $92.30   9.117%   $100.715   $100.72   $100.70   $100.70  
  Purchase #5 $61.32   11.621%   $68.446   $68.45   $68.45   $68.40  
  Purchase #6 $244.68   11.783%   $273.5106   $273.51   $273.50   $273.50  
  Purchase #7 $76.78   12.475%   $86.3583   $86.36   $86.35   $86.40  
  7 purchase totals = $774.79       $850.8281   $850.83   $850.75   $850.80