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 $114.92   8.543%   $124.7376   $124.74   $124.75   $124.70  
  Purchase #2 $56.77   12.770%   $64.0195   $64.02   $64.00   $64.00  
  Purchase #3 $19.34   6.678%   $20.6315   $20.63   $20.65   $20.60  
  Purchase #4 $187.25   3.282%   $193.3955   $193.40   $193.40   $193.40  
  Purchase #5 $140.30   4.680%   $146.866   $146.87   $146.85   $146.90  
  Purchase #6 $126.78   4.576%   $132.5815   $132.58   $132.60   $132.60  
  Purchase #7 $29.25   11.292%   $32.5529   $32.55   $32.55   $32.60  
  7 purchase totals = $674.61       $714.7845   $714.79   $714.80   $714.80