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 $245.70   6.611%   $261.9432   $261.94   $261.95   $261.90  
  Purchase #2 $209.41   7.138%   $224.3577   $224.36   $224.35   $224.40  
  Purchase #3 $132.67   6.359%   $141.1065   $141.11   $141.10   $141.10  
  Purchase #4 $123.78   8.768%   $134.633   $134.63   $134.65   $134.60  
  Purchase #5 $191.54   11.734%   $214.0153   $214.02   $214.00   $214.00  
  Purchase #6 $202.79   8.201%   $219.4208   $219.42   $219.40   $219.40  
  Purchase #7 $223.78   12.210%   $251.1035   $251.10   $251.10   $251.10  
  7 purchase totals = $1,329.67       $1,446.5800   $1,446.58   $1,446.55   $1,446.50