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 $58.60   13.778%   $66.6739   $66.67   $66.65   $66.70  
  Purchase #2 $156.91   13.445%   $178.0065   $178.01   $178.00   $178.00  
  Purchase #3 $130.38   10.381%   $143.9147   $143.91   $143.90   $143.90  
  Purchase #4 $202.78   4.837%   $212.5885   $212.59   $212.60   $212.60  
  Purchase #5 $164.32   6.482%   $174.9712   $174.97   $174.95   $175.00  
  Purchase #6 $63.38   3.498%   $65.597   $65.60   $65.60   $65.60  
  Purchase #7 $70.79   3.479%   $73.2528   $73.25   $73.25   $73.30  
  7 purchase totals = $847.16       $915.0046   $915.00   $914.95   $915.10