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	$244.62	10.812%	$271.0683	$271.07	$271.05	$271.10
Purchase #2	$189.29	4.546%	$197.8951	$197.90	$197.90	$197.90
Purchase #3	$179.91	5.328%	$189.4956	$189.50	$189.50	$189.50
Purchase #4	$59.27	11.568%	$66.1264	$66.13	$66.15	$66.10
Purchase #5	$38.25	6.721%	$40.8208	$40.82	$40.80	$40.80
Purchase #6	$141.58	6.448%	$150.7091	$150.71	$150.70	$150.70
Purchase #7	$64.77	8.294%	$70.142	$70.14	$70.15	$70.10
7 purchase totals =	$917.69		$986.2573	$986.27	$986.25	$986.20