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 $221.63   11.421%   $246.9424   $246.94   $246.95   $246.90  
  Purchase #2 $182.86   6.586%   $194.9032   $194.90   $194.90   $194.90  
  Purchase #3 $203.46   10.626%   $225.0797   $225.08   $225.10   $225.10  
  Purchase #4 $245.77   6.435%   $261.5853   $261.59   $261.60   $261.60  
  Purchase #5 $16.82   6.642%   $17.9372   $17.94   $17.95   $17.90  
  Purchase #6 $152.40   13.560%   $173.0654   $173.07   $173.05   $173.10  
  Purchase #7 $148.85   5.265%   $156.687   $156.69   $156.70   $156.70  
  7 purchase totals = $1,171.79       $1,276.2002   $1,276.21   $1,276.25   $1,276.20