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 $238.33   11.723%   $266.2694   $266.27   $266.25   $266.30  
  Purchase #2 $68.46   11.629%   $76.4212   $76.42   $76.40   $76.40  
  Purchase #3 $250.87   10.455%   $277.0985   $277.10   $277.10   $277.10  
  Purchase #4 $112.40   12.317%   $126.2443   $126.24   $126.25   $126.20  
  Purchase #5 $96.31   11.722%   $107.5995   $107.60   $107.60   $107.60  
  Purchase #6 $111.76   7.352%   $119.9766   $119.98   $120.00   $120.00  
  Purchase #7 $238.26   12.476%   $267.9853   $267.99   $268.00   $268.00  
  7 purchase totals = $1,116.39       $1,241.5948   $1,241.60   $1,241.60   $1,241.60