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 $123.99   3.414%   $128.223   $128.22   $128.20   $128.20  
  Purchase #2 $8.64   7.650%   $9.301   $9.30   $9.30   $9.30  
  Purchase #3 $129.57   10.480%   $143.1489   $143.15   $143.15   $143.10  
  Purchase #4 $178.29   5.747%   $188.5363   $188.54   $188.55   $188.50  
  Purchase #5 $13.25   13.143%   $14.9914   $14.99   $15.00   $15.00  
  Purchase #6 $60.50   7.810%   $65.2251   $65.23   $65.25   $65.20  
  Purchase #7 $71.60   6.482%   $76.2411   $76.24   $76.25   $76.20  
  7 purchase totals = $585.84       $625.6668   $625.67   $625.70   $625.50