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	$115.67	10.209%	$127.4788	$127.48	$127.50	$127.50
Purchase #2	$78.93	5.536%	$83.2996	$83.30	$83.30	$83.30
Purchase #3	$13.41	6.804%	$14.3224	$14.32	$14.30	$14.30
Purchase #4	$233.91	4.818%	$245.1798	$245.18	$245.20	$245.20
Purchase #5	$64.65	11.867%	$72.322	$72.32	$72.30	$72.30
Purchase #6	$11.84	5.265%	$12.4634	$12.46	$12.45	$12.50
Purchase #7	$21.33	12.372%	$23.9689	$23.97	$23.95	$24.00
7 purchase totals =	$539.74		$579.0349	$579.03	$579.00	$579.10