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	$50.46	9.274%	$55.1397	$55.14	$55.15	$55.10
Purchase #2	$60.93	7.123%	$65.27	$65.27	$65.25	$65.30
Purchase #3	$228.64	8.538%	$248.1613	$248.16	$248.15	$248.20
Purchase #4	$139.39	8.166%	$150.7726	$150.77	$150.75	$150.80
Purchase #5	$68.68	10.396%	$75.82	$75.82	$75.80	$75.80
Purchase #6	$240.43	10.562%	$265.8242	$265.82	$265.80	$265.80
Purchase #7	$33.50	12.564%	$37.7089	$37.71	$37.70	$37.70
7 purchase totals =	$822.03		$898.6967	$898.69	$898.60	$898.70