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 $29.36   11.602%   $32.7663   $32.77   $32.75   $32.80  
  Purchase #2 $121.94   3.210%   $125.8543   $125.85   $125.85   $125.90  
  Purchase #3 $220.65   13.694%   $250.8658   $250.87   $250.85   $250.90  
  Purchase #4 $168.71   13.405%   $191.3256   $191.33   $191.35   $191.30  
  Purchase #5 $249.91   10.612%   $276.4304   $276.43   $276.45   $276.40  
  Purchase #6 $132.90   10.195%   $146.4492   $146.45   $146.45   $146.40  
  Purchase #7 $167.73   7.442%   $180.2125   $180.21   $180.20   $180.20  
  7 purchase totals = $1,091.20       $1,203.9041   $1,203.91   $1,203.90   $1,203.90