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 $241.32   6.211%   $256.3084   $256.31   $256.30   $256.30  
  Purchase #2 $145.94   9.302%   $159.5153   $159.52   $159.50   $159.50  
  Purchase #3 $47.72   6.857%   $50.9922   $50.99   $51.00   $51.00  
  Purchase #4 $35.52   9.328%   $38.8333   $38.83   $38.85   $38.80  
  Purchase #5 $97.71   9.579%   $107.0696   $107.07   $107.05   $107.10  
  Purchase #6 $200.34   13.178%   $226.7408   $226.74   $226.75   $226.70  
  Purchase #7 $182.50   8.210%   $197.4833   $197.48   $197.50   $197.50  
  7 purchase totals = $951.05       $1,036.9429   $1,036.94   $1,036.95   $1,036.90