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 $117.26   8.580%   $127.3209   $127.32   $127.30   $127.30  
  Purchase #2 $95.41   4.473%   $99.6777   $99.68   $99.70   $99.70  
  Purchase #3 $49.99   11.813%   $55.8953   $55.90   $55.90   $55.90  
  Purchase #4 $24.51   10.734%   $27.1409   $27.14   $27.15   $27.10  
  Purchase #5 $244.80   5.375%   $257.958   $257.96   $257.95   $258.00  
  Purchase #6 $170.59   7.555%   $183.4781   $183.48   $183.50   $183.50  
  Purchase #7 $24.38   10.602%   $26.9648   $26.96   $26.95   $27.00  
  7 purchase totals = $726.94       $778.4357   $778.44   $778.45   $778.50