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 $119.46   11.760%   $133.5085   $133.51   $133.50   $133.50  
  Purchase #2 $78.36   10.521%   $86.6043   $86.60   $86.60   $86.60  
  Purchase #3 $240.49   5.750%   $254.3182   $254.32   $254.30   $254.30  
  Purchase #4 $154.73   8.367%   $167.6763   $167.68   $167.70   $167.70  
  Purchase #5 $182.34   12.425%   $204.9957   $205.00   $205.00   $205.00  
  Purchase #6 $6.96   6.742%   $7.4292   $7.43   $7.45   $7.40  
  Purchase #7 $128.91   3.135%   $132.9513   $132.95   $132.95   $133.00  
  7 purchase totals = $911.25       $987.4835   $987.49   $987.50   $987.50