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 $114.26   6.263%   $121.4161   $121.42   $121.40   $121.40  
  Purchase #2 $234.97   11.763%   $262.6095   $262.61   $262.60   $262.60  
  Purchase #3 $26.38   6.606%   $28.1227   $28.12   $28.10   $28.10  
  Purchase #4 $247.84   9.742%   $271.9846   $271.98   $272.00   $272.00  
  Purchase #5 $20.75   6.760%   $22.1527   $22.15   $22.15   $22.20  
  Purchase #6 $32.47   6.377%   $34.5406   $34.54   $34.55   $34.50  
  Purchase #7 $11.86   5.141%   $12.4697   $12.47   $12.45   $12.50  
  7 purchase totals = $688.53       $753.2959   $753.29   $753.25   $753.30