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 $111.63   6.400%   $118.7743   $118.77   $118.75   $118.80  
  Purchase #2 $60.38   4.150%   $62.8858   $62.89   $62.90   $62.90  
  Purchase #3 $235.43   4.614%   $246.2927   $246.29   $246.30   $246.30  
  Purchase #4 $9.29   13.583%   $10.5519   $10.55   $10.55   $10.60  
  Purchase #5 $89.32   3.868%   $92.7749   $92.77   $92.75   $92.80  
  Purchase #6 $154.96   5.797%   $163.943   $163.94   $163.95   $163.90  
  Purchase #7 $12.53   11.775%   $14.0054   $14.01   $14.00   $14.00  
  7 purchase totals = $673.54       $709.2280   $709.22   $709.20   $709.30