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 $54.60   12.652%   $61.508   $61.51   $61.50   $61.50  
  Purchase #2 $47.95   9.160%   $52.3422   $52.34   $52.35   $52.30  
  Purchase #3 $67.40   11.317%   $75.0277   $75.03   $75.05   $75.00  
  Purchase #4 $105.51   8.181%   $114.1418   $114.14   $114.15   $114.10  
  Purchase #5 $114.89   13.659%   $130.5828   $130.58   $130.60   $130.60  
  Purchase #6 $156.44   9.461%   $171.2408   $171.24   $171.25   $171.20  
  Purchase #7 $202.62   11.703%   $226.3326   $226.33   $226.35   $226.30  
  7 purchase totals = $749.41       $831.1759   $831.17   $831.25   $831.00