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 $89.51   5.526%   $94.4563   $94.46   $94.45   $94.50  
  Purchase #2 $228.96   9.627%   $251.002   $251.00   $251.00   $251.00  
  Purchase #3 $207.46   13.761%   $236.0086   $236.01   $236.00   $236.00  
  Purchase #4 $174.57   11.298%   $194.2929   $194.29   $194.30   $194.30  
  Purchase #5 $162.53   9.635%   $178.1898   $178.19   $178.20   $178.20  
  Purchase #6 $8.26   8.720%   $8.9803   $8.98   $9.00   $9.00  
  Purchase #7 $182.59   13.256%   $206.7941   $206.79   $206.80   $206.80  
  7 purchase totals = $1,053.88       $1,169.7240   $1,169.72   $1,169.75   $1,169.80