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 $169.39   13.165%   $191.6902   $191.69   $191.70   $191.70  
  Purchase #2 $209.82   12.535%   $236.1209   $236.12   $236.10   $236.10  
  Purchase #3 $119.39   5.220%   $125.6222   $125.62   $125.60   $125.60  
  Purchase #4 $202.88   6.785%   $216.6454   $216.65   $216.65   $216.60  
  Purchase #5 $213.51   7.430%   $229.3738   $229.37   $229.35   $229.40  
  Purchase #6 $189.28   11.443%   $210.9393   $210.94   $210.95   $210.90  
  Purchase #7 $84.94   8.382%   $92.0597   $92.06   $92.05   $92.10  
  7 purchase totals = $1,189.21       $1,302.4515   $1,302.45   $1,302.40   $1,302.40