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 $202.33   10.466%   $223.5059   $223.51   $223.50   $223.50  
  Purchase #2 $19.40   9.135%   $21.1722   $21.17   $21.15   $21.20  
  Purchase #3 $144.84   4.293%   $151.058   $151.06   $151.05   $151.10  
  Purchase #4 $69.92   12.629%   $78.7502   $78.75   $78.75   $78.80  
  Purchase #5 $65.47   12.117%   $73.403   $73.40   $73.40   $73.40  
  Purchase #6 $241.34   13.810%   $274.6691   $274.67   $274.65   $274.70  
  Purchase #7 $118.89   9.246%   $129.8826   $129.88   $129.90   $129.90  
  7 purchase totals = $862.19       $952.4410   $952.44   $952.40   $952.60