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 $218.56   12.533%   $245.9521   $245.95   $245.95   $246.00  
  Purchase #2 $107.87   10.674%   $119.384   $119.38   $119.40   $119.40  
  Purchase #3 $111.36   9.395%   $121.8223   $121.82   $121.80   $121.80  
  Purchase #4 $214.74   12.598%   $241.7929   $241.79   $241.80   $241.80  
  Purchase #5 $82.48   9.569%   $90.3725   $90.37   $90.35   $90.40  
  Purchase #6 $152.40   12.226%   $171.0324   $171.03   $171.05   $171.00  
  Purchase #7 $66.36   6.105%   $70.4113   $70.41   $70.40   $70.40  
  7 purchase totals = $953.77       $1,060.7675   $1,060.75   $1,060.75   $1,060.80