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 $182.59   10.495%   $201.7528   $201.75   $201.75   $201.80  
  Purchase #2 $180.68   4.243%   $188.3463   $188.35   $188.35   $188.30  
  Purchase #3 $236.38   13.135%   $267.4285   $267.43   $267.45   $267.40  
  Purchase #4 $71.45   4.217%   $74.463   $74.46   $74.45   $74.50  
  Purchase #5 $57.42   5.126%   $60.3633   $60.36   $60.35   $60.40  
  Purchase #6 $167.42   6.304%   $177.9742   $177.97   $177.95   $178.00  
  Purchase #7 $13.44   6.252%   $14.2803   $14.28   $14.30   $14.30  
  7 purchase totals = $909.38       $984.6084   $984.60   $984.60   $984.70