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 $56.86   12.417%   $63.9203   $63.92   $63.90   $63.90  
  Purchase #2 $113.60   11.632%   $126.814   $126.81   $126.80   $126.80  
  Purchase #3 $248.76   8.274%   $269.3424   $269.34   $269.35   $269.30  
  Purchase #4 $75.53   11.838%   $84.4712   $84.47   $84.45   $84.50  
  Purchase #5 $171.83   13.823%   $195.5821   $195.58   $195.60   $195.60  
  Purchase #6 $224.90   11.378%   $250.4891   $250.49   $250.50   $250.50  
  Purchase #7 $206.83   13.761%   $235.2919   $235.29   $235.30   $235.30  
  7 purchase totals = $1,098.31       $1,225.9110   $1,225.90   $1,225.90   $1,225.90