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 $216.77   3.211%   $223.7305   $223.73   $223.75   $223.70  
  Purchase #2 $134.93   12.416%   $151.6829   $151.68   $151.70   $151.70  
  Purchase #3 $52.40   10.234%   $57.7626   $57.76   $57.75   $57.80  
  Purchase #4 $184.44   3.189%   $190.3218   $190.32   $190.30   $190.30  
  Purchase #5 $246.51   8.363%   $267.1256   $267.13   $267.15   $267.10  
  Purchase #6 $6.42   12.408%   $7.2166   $7.22   $7.20   $7.20  
  Purchase #7 $69.40   12.694%   $78.2096   $78.21   $78.20   $78.20  
  7 purchase totals = $910.87       $976.0496   $976.05   $976.05   $976.00