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 $69.75   6.669%   $74.4016   $74.40   $74.40   $74.40  
  Purchase #2 $113.79   9.476%   $124.5727   $124.57   $124.55   $124.60  
  Purchase #3 $29.56   11.587%   $32.9851   $32.99   $33.00   $33.00  
  Purchase #4 $98.54   13.386%   $111.7306   $111.73   $111.75   $111.70  
  Purchase #5 $137.57   13.731%   $156.4597   $156.46   $156.45   $156.50  
  Purchase #6 $236.32   4.413%   $246.7488   $246.75   $246.75   $246.70  
  Purchase #7 $199.84   5.439%   $210.7093   $210.71   $210.70   $210.70  
  7 purchase totals = $885.37       $957.6078   $957.61   $957.60   $957.60