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 $86.35   10.211%   $95.1672   $95.17   $95.15   $95.20  
  Purchase #2 $10.68   9.227%   $11.6654   $11.67   $11.65   $11.70  
  Purchase #3 $112.38   7.626%   $120.9501   $120.95   $120.95   $121.00  
  Purchase #4 $197.70   8.813%   $215.1233   $215.12   $215.10   $215.10  
  Purchase #5 $23.47   11.580%   $26.1878   $26.19   $26.20   $26.20  
  Purchase #6 $232.33   12.820%   $262.1147   $262.11   $262.10   $262.10  
  Purchase #7 $231.96   12.691%   $261.398   $261.40   $261.40   $261.40  
  7 purchase totals = $894.87       $992.6065   $992.61   $992.55   $992.70