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 $159.30   10.671%   $176.2989   $176.30   $176.30   $176.30  
  Purchase #2 $244.63   8.468%   $265.3453   $265.35   $265.35   $265.30  
  Purchase #3 $28.66   11.494%   $31.9542   $31.95   $31.95   $32.00  
  Purchase #4 $147.31   11.561%   $164.3405   $164.34   $164.35   $164.30  
  Purchase #5 $56.59   8.557%   $61.4324   $61.43   $61.45   $61.40  
  Purchase #6 $72.97   5.459%   $76.9534   $76.95   $76.95   $77.00  
  Purchase #7 $249.38   4.320%   $260.1532   $260.15   $260.15   $260.20  
  7 purchase totals = $958.84       $1,036.4779   $1,036.47   $1,036.50   $1,036.50