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 $53.84   12.477%   $60.5576   $60.56   $60.55   $60.60  
  Purchase #2 $13.30   5.353%   $14.0119   $14.01   $14.00   $14.00  
  Purchase #3 $111.74   8.149%   $120.8457   $120.85   $120.85   $120.80  
  Purchase #4 $236.88   10.164%   $260.9565   $260.96   $260.95   $261.00  
  Purchase #5 $247.32   7.620%   $266.1658   $266.17   $266.15   $266.20  
  Purchase #6 $43.50   12.206%   $48.8096   $48.81   $48.80   $48.80  
  Purchase #7 $217.76   13.438%   $247.0226   $247.02   $247.00   $247.00  
  7 purchase totals = $924.34       $1,018.3697   $1,018.38   $1,018.30   $1,018.40