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 $59.98   12.329%   $67.3749   $67.37   $67.35   $67.40  
  Purchase #2 $92.45   5.613%   $97.6392   $97.64   $97.65   $97.60  
  Purchase #3 $14.95   11.487%   $16.6673   $16.67   $16.65   $16.70  
  Purchase #4 $227.90   8.546%   $247.3763   $247.38   $247.40   $247.40  
  Purchase #5 $227.68   6.239%   $241.885   $241.89   $241.90   $241.90  
  Purchase #6 $99.69   8.106%   $107.7709   $107.77   $107.75   $107.80  
  Purchase #7 $135.68   8.255%   $146.8804   $146.88   $146.90   $146.90  
  7 purchase totals = $858.33       $925.5940   $925.60   $925.60   $925.70