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 $246.97   3.368%   $255.2879   $255.29   $255.30   $255.30  
  Purchase #2 $184.36   9.794%   $202.4162   $202.42   $202.40   $202.40  
  Purchase #3 $52.58   3.821%   $54.5891   $54.59   $54.60   $54.60  
  Purchase #4 $208.98   11.307%   $232.6094   $232.61   $232.60   $232.60  
  Purchase #5 $173.35   12.357%   $194.7709   $194.77   $194.75   $194.80  
  Purchase #6 $195.51   9.619%   $214.3161   $214.32   $214.30   $214.30  
  Purchase #7 $241.63   7.655%   $260.1268   $260.13   $260.15   $260.10  
  7 purchase totals = $1,303.38       $1,414.1164   $1,414.13   $1,414.10   $1,414.10