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 $41.74   6.216%   $44.3346   $44.33   $44.35   $44.30  
  Purchase #2 $184.46   13.676%   $209.6867   $209.69   $209.70   $209.70  
  Purchase #3 $104.34   11.595%   $116.4382   $116.44   $116.45   $116.40  
  Purchase #4 $223.36   11.864%   $249.8594   $249.86   $249.85   $249.90  
  Purchase #5 $157.45   12.181%   $176.629   $176.63   $176.65   $176.60  
  Purchase #6 $227.46   6.563%   $242.3882   $242.39   $242.40   $242.40  
  Purchase #7 $54.88   4.329%   $57.2558   $57.26   $57.25   $57.30  
  7 purchase totals = $993.69       $1,096.5919   $1,096.60   $1,096.65   $1,096.60