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 $61.96   10.730%   $68.6083   $68.61   $68.60   $68.60  
  Purchase #2 $227.97   5.489%   $240.4833   $240.48   $240.50   $240.50  
  Purchase #3 $70.66   11.721%   $78.9421   $78.94   $78.95   $78.90  
  Purchase #4 $70.39   10.273%   $77.6212   $77.62   $77.60   $77.60  
  Purchase #5 $204.66   12.227%   $229.6838   $229.68   $229.70   $229.70  
  Purchase #6 $41.49   9.649%   $45.4934   $45.49   $45.50   $45.50  
  Purchase #7 $56.99   8.200%   $61.6632   $61.66   $61.65   $61.70  
  7 purchase totals = $734.12       $802.4953   $802.48   $802.50   $802.50