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 $199.28   8.275%   $215.7704   $215.77   $215.75   $215.80  
  Purchase #2 $156.81   12.142%   $175.8499   $175.85   $175.85   $175.80  
  Purchase #3 $242.99   7.499%   $261.2118   $261.21   $261.20   $261.20  
  Purchase #4 $224.29   8.188%   $242.6549   $242.65   $242.65   $242.70  
  Purchase #5 $245.43   9.366%   $268.417   $268.42   $268.40   $268.40  
  Purchase #6 $15.84   11.703%   $17.6938   $17.69   $17.70   $17.70  
  Purchase #7 $210.64   10.142%   $232.0031   $232.00   $232.00   $232.00  
  7 purchase totals = $1,295.28       $1,413.6009   $1,413.59   $1,413.55   $1,413.60