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 $162.79   11.805%   $182.0074   $182.01   $182.00   $182.00  
  Purchase #2 $47.91   13.414%   $54.3366   $54.34   $54.35   $54.30  
  Purchase #3 $200.59   12.620%   $225.9045   $225.90   $225.90   $225.90  
  Purchase #4 $244.44   4.858%   $256.3149   $256.31   $256.30   $256.30  
  Purchase #5 $151.26   10.799%   $167.5946   $167.59   $167.60   $167.60  
  Purchase #6 $248.59   3.582%   $257.4945   $257.49   $257.50   $257.50  
  Purchase #7 $70.93   8.158%   $76.7165   $76.72   $76.70   $76.70  
  7 purchase totals = $1,126.51       $1,220.3690   $1,220.36   $1,220.35   $1,220.30