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 $188.92   8.306%   $204.6117   $204.61   $204.60   $204.60  
  Purchase #2 $159.91   9.250%   $174.7017   $174.70   $174.70   $174.70  
  Purchase #3 $121.62   6.229%   $129.1957   $129.20   $129.20   $129.20  
  Purchase #4 $109.34   3.219%   $112.8597   $112.86   $112.85   $112.90  
  Purchase #5 $208.70   13.528%   $236.9329   $236.93   $236.95   $236.90  
  Purchase #6 $60.71   10.308%   $66.968   $66.97   $66.95   $67.00  
  Purchase #7 $126.30   12.657%   $142.2858   $142.29   $142.30   $142.30  
  7 purchase totals = $975.50       $1,067.5555   $1,067.56   $1,067.55   $1,067.60