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	$129.89	11.154%	$144.3779	$144.38	$144.40	$144.40
Purchase #2	$250.45	5.151%	$263.3507	$263.35	$263.35	$263.40
Purchase #3	$72.50	13.728%	$82.4528	$82.45	$82.45	$82.50
Purchase #4	$107.40	3.425%	$111.0785	$111.08	$111.10	$111.10
Purchase #5	$203.53	3.134%	$209.9086	$209.91	$209.90	$209.90
Purchase #6	$29.69	12.550%	$33.4161	$33.42	$33.40	$33.40
Purchase #7	$44.73	7.519%	$48.0932	$48.09	$48.10	$48.10
7 purchase totals =	$838.19		$892.6778	$892.68	$892.70	$892.80