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 $22.84   8.388%   $24.7558   $24.76   $24.75   $24.80  
  Purchase #2 $198.68   7.624%   $213.8274   $213.83   $213.85   $213.80  
  Purchase #3 $174.38   8.256%   $188.7768   $188.78   $188.80   $188.80  
  Purchase #4 $215.73   12.784%   $243.3089   $243.31   $243.30   $243.30  
  Purchase #5 $56.87   3.687%   $58.9668   $58.97   $58.95   $59.00  
  Purchase #6 $141.89   4.799%   $148.6993   $148.70   $148.70   $148.70  
  Purchase #7 $56.43   11.182%   $62.74   $62.74   $62.75   $62.70  
  7 purchase totals = $866.82       $941.0750   $941.09   $941.10   $941.10