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 $246.42   3.408%   $254.818   $254.82   $254.80   $254.80  
  Purchase #2 $54.54   7.604%   $58.6872   $58.69   $58.70   $58.70  
  Purchase #3 $153.91   7.336%   $165.2008   $165.20   $165.20   $165.20  
  Purchase #4 $35.47   5.326%   $37.3591   $37.36   $37.35   $37.40  
  Purchase #5 $107.26   11.833%   $119.9521   $119.95   $119.95   $120.00  
  Purchase #6 $192.95   9.614%   $211.5002   $211.50   $211.50   $211.50  
  Purchase #7 $20.50   4.382%   $21.3983   $21.40   $21.40   $21.40  
  7 purchase totals = $811.05       $868.9157   $868.92   $868.90   $869.00