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 $51.37   13.228%   $58.1652   $58.17   $58.15   $58.20  
  Purchase #2 $207.54   8.521%   $225.2245   $225.22   $225.20   $225.20  
  Purchase #3 $212.86   13.760%   $242.1495   $242.15   $242.15   $242.10  
  Purchase #4 $101.44   11.130%   $112.7303   $112.73   $112.75   $112.70  
  Purchase #5 $163.33   9.725%   $179.2138   $179.21   $179.20   $179.20  
  Purchase #6 $132.33   11.394%   $147.4077   $147.41   $147.40   $147.40  
  Purchase #7 $19.42   3.558%   $20.111   $20.11   $20.10   $20.10  
  7 purchase totals = $888.29       $985.0020   $985.00   $984.95   $984.90