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 $60.56   9.439%   $66.2763   $66.28   $66.30   $66.30  
  Purchase #2 $213.97   5.392%   $225.5073   $225.51   $225.50   $225.50  
  Purchase #3 $113.62   6.320%   $120.8008   $120.80   $120.80   $120.80  
  Purchase #4 $228.78   9.393%   $250.2693   $250.27   $250.25   $250.30  
  Purchase #5 $224.80   5.381%   $236.8965   $236.90   $236.90   $236.90  
  Purchase #6 $241.29   8.208%   $261.0951   $261.10   $261.10   $261.10  
  Purchase #7 $68.85   6.810%   $73.5387   $73.54   $73.55   $73.50  
  7 purchase totals = $1,151.87       $1,234.3840   $1,234.40   $1,234.40   $1,234.40