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 $217.65   3.603%   $225.4919   $225.49   $225.50   $225.50  
  Purchase #2 $195.68   10.716%   $216.6491   $216.65   $216.65   $216.60  
  Purchase #3 $82.68   13.853%   $94.1337   $94.13   $94.15   $94.10  
  Purchase #4 $237.70   4.159%   $247.5859   $247.59   $247.60   $247.60  
  Purchase #5 $194.64   3.172%   $200.814   $200.81   $200.80   $200.80  
  Purchase #6 $165.61   13.544%   $188.0402   $188.04   $188.05   $188.00  
  Purchase #7 $119.32   6.216%   $126.7369   $126.74   $126.75   $126.70  
  7 purchase totals = $1,213.28       $1,299.4517   $1,299.45   $1,299.50   $1,299.30