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 $242.92   12.222%   $272.6097   $272.61   $272.60   $272.60  
  Purchase #2 $134.96   7.664%   $145.3033   $145.30   $145.30   $145.30  
  Purchase #3 $62.77   5.255%   $66.0686   $66.07   $66.05   $66.10  
  Purchase #4 $135.82   5.315%   $143.0388   $143.04   $143.05   $143.00  
  Purchase #5 $179.63   9.677%   $197.0128   $197.01   $197.00   $197.00  
  Purchase #6 $219.42   12.181%   $246.1476   $246.15   $246.15   $246.10  
  Purchase #7 $47.41   12.834%   $53.4946   $53.49   $53.50   $53.50  
  7 purchase totals = $1,022.93       $1,123.6754   $1,123.67   $1,123.65   $1,123.60