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 $68.28   9.807%   $74.9762   $74.98   $75.00   $75.00  
  Purchase #2 $119.85   4.332%   $125.0419   $125.04   $125.05   $125.00  
  Purchase #3 $65.99   10.457%   $72.8906   $72.89   $72.90   $72.90  
  Purchase #4 $98.44   11.246%   $109.5106   $109.51   $109.50   $109.50  
  Purchase #5 $12.76   5.849%   $13.5063   $13.51   $13.50   $13.50  
  Purchase #6 $21.70   8.750%   $23.5988   $23.60   $23.60   $23.60  
  Purchase #7 $53.31   9.581%   $58.4176   $58.42   $58.40   $58.40  
  7 purchase totals = $440.33       $477.9420   $477.95   $477.95   $477.90