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 $48.83   4.311%   $50.9351   $50.94   $50.95   $50.90  
  Purchase #2 $126.72   10.278%   $139.7443   $139.74   $139.75   $139.70  
  Purchase #3 $244.40   8.232%   $264.519   $264.52   $264.50   $264.50  
  Purchase #4 $108.86   13.422%   $123.4712   $123.47   $123.45   $123.50  
  Purchase #5 $194.39   9.542%   $212.9387   $212.94   $212.95   $212.90  
  Purchase #6 $214.37   12.174%   $240.4674   $240.47   $240.45   $240.50  
  Purchase #7 $200.77   9.478%   $219.799   $219.80   $219.80   $219.80  
  7 purchase totals = $1,138.34       $1,251.8747   $1,251.88   $1,251.85   $1,251.80