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 $146.52   12.412%   $164.7061   $164.71   $164.70   $164.70  
  Purchase #2 $234.50   7.125%   $251.2081   $251.21   $251.20   $251.20  
  Purchase #3 $161.71   12.690%   $182.231   $182.23   $182.25   $182.20  
  Purchase #4 $10.34   10.541%   $11.4299   $11.43   $11.45   $11.40  
  Purchase #5 $60.62   3.450%   $62.7114   $62.71   $62.70   $62.70  
  Purchase #6 $236.35   10.217%   $260.4979   $260.50   $260.50   $260.50  
  Purchase #7 $23.60   12.718%   $26.6014   $26.60   $26.60   $26.60  
  7 purchase totals = $873.64       $959.3858   $959.39   $959.40   $959.30