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	$36.95	4.374%	$38.5662	$38.57	$38.55	$38.60
Purchase #2	$56.88	7.811%	$61.3229	$61.32	$61.30	$61.30
Purchase #3	$247.41	11.399%	$275.6123	$275.61	$275.60	$275.60
Purchase #4	$58.87	3.464%	$60.9093	$60.91	$60.90	$60.90
Purchase #5	$66.91	4.675%	$70.038	$70.04	$70.05	$70.00
Purchase #6	$25.51	8.566%	$27.6952	$27.70	$27.70	$27.70
Purchase #7	$46.78	13.448%	$53.071	$53.07	$53.05	$53.10
7 purchase totals =	$539.31		$587.2149	$587.22	$587.15	$587.20