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 $58.97   8.782%   $64.1487   $64.15   $64.15   $64.10  
  Purchase #2 $115.25   3.788%   $119.6157   $119.62   $119.60   $119.60  
  Purchase #3 $13.54   13.543%   $15.3737   $15.37   $15.35   $15.40  
  Purchase #4 $132.30   4.515%   $138.2733   $138.27   $138.25   $138.30  
  Purchase #5 $212.76   3.133%   $219.4258   $219.43   $219.45   $219.40  
  Purchase #6 $32.81   12.741%   $36.9903   $36.99   $37.00   $37.00  
  Purchase #7 $128.80   8.797%   $140.1305   $140.13   $140.15   $140.10  
  7 purchase totals = $694.43       $733.9580   $733.96   $733.95   $733.90