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 $67.63   9.283%   $73.9081   $73.91   $73.90   $73.90  
  Purchase #2 $201.46   13.384%   $228.4234   $228.42   $228.40   $228.40  
  Purchase #3 $47.25   6.733%   $50.4313   $50.43   $50.45   $50.40  
  Purchase #4 $174.84   11.132%   $194.3032   $194.30   $194.30   $194.30  
  Purchase #5 $111.73   5.204%   $117.5444   $117.54   $117.55   $117.50  
  Purchase #6 $212.29   8.145%   $229.581   $229.58   $229.60   $229.60  
  Purchase #7 $79.48   13.653%   $90.3314   $90.33   $90.35   $90.30  
  7 purchase totals = $894.68       $984.5228   $984.51   $984.55   $984.40