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	$52.71	4.511%	$55.0877	$55.09	$55.10	$55.10
Purchase #2	$238.89	13.660%	$271.5224	$271.52	$271.50	$271.50
Purchase #3	$37.71	8.539%	$40.9301	$40.93	$40.95	$40.90
Purchase #4	$45.90	10.192%	$50.5781	$50.58	$50.60	$50.60
Purchase #5	$57.42	6.814%	$61.3326	$61.33	$61.35	$61.30
Purchase #6	$179.74	8.765%	$195.4942	$195.49	$195.50	$195.50
Purchase #7	$189.95	4.434%	$198.3724	$198.37	$198.35	$198.40
7 purchase totals =	$802.32		$873.3175	$873.31	$873.35	$873.30