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 $234.48   5.468%   $247.3014   $247.30   $247.30   $247.30  
  Purchase #2 $12.51   10.193%   $13.7851   $13.79   $13.80   $13.80  
  Purchase #3 $211.87   11.591%   $236.4279   $236.43   $236.45   $236.40  
  Purchase #4 $94.33   10.299%   $104.045   $104.05   $104.05   $104.00  
  Purchase #5 $136.53   8.807%   $148.5542   $148.55   $148.55   $148.60  
  Purchase #6 $232.78   7.624%   $250.5271   $250.53   $250.55   $250.50  
  Purchase #7 $107.96   10.242%   $119.0173   $119.02   $119.00   $119.00  
  7 purchase totals = $1,030.46       $1,119.6580   $1,119.67   $1,119.70   $1,119.60