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 $22.68   13.171%   $25.6672   $25.67   $25.65   $25.70  
  Purchase #2 $200.72   8.797%   $218.3773   $218.38   $218.40   $218.40  
  Purchase #3 $152.34   11.566%   $169.9596   $169.96   $169.95   $170.00  
  Purchase #4 $208.60   12.436%   $234.5415   $234.54   $234.55   $234.50  
  Purchase #5 $173.77   5.132%   $182.6879   $182.69   $182.70   $182.70  
  Purchase #6 $248.27   4.813%   $260.2192   $260.22   $260.20   $260.20  
  Purchase #7 $247.77   6.269%   $263.3027   $263.30   $263.30   $263.30  
  7 purchase totals = $1,254.15       $1,354.7554   $1,354.76   $1,354.75   $1,354.80