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 $228.95   7.595%   $246.3388   $246.34   $246.35   $246.30  
  Purchase #2 $215.55   12.647%   $242.8106   $242.81   $242.80   $242.80  
  Purchase #3 $65.43   12.540%   $73.6349   $73.63   $73.65   $73.60  
  Purchase #4 $86.90   7.140%   $93.1047   $93.10   $93.10   $93.10  
  Purchase #5 $223.93   8.292%   $242.4983   $242.50   $242.50   $242.50  
  Purchase #6 $131.32   11.197%   $146.0239   $146.02   $146.00   $146.00  
  Purchase #7 $95.64   6.617%   $101.9685   $101.97   $101.95   $102.00  
  7 purchase totals = $1,047.72       $1,146.3797   $1,146.37   $1,146.35   $1,146.30