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 $48.89   4.843%   $51.2577   $51.26   $51.25   $51.30  
  Purchase #2 $146.66   11.772%   $163.9248   $163.92   $163.90   $163.90  
  Purchase #3 $163.45   4.754%   $171.2204   $171.22   $171.20   $171.20  
  Purchase #4 $44.94   5.800%   $47.5465   $47.55   $47.55   $47.50  
  Purchase #5 $134.74   11.686%   $150.4857   $150.49   $150.50   $150.50  
  Purchase #6 $193.25   6.573%   $205.9523   $205.95   $205.95   $206.00  
  Purchase #7 $244.77   13.475%   $277.7528   $277.75   $277.75   $277.80  
  7 purchase totals = $976.70       $1,068.1402   $1,068.14   $1,068.10   $1,068.20