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	$243.28	11.442%	$271.1161	$271.12	$271.10	$271.10
Purchase #2	$54.46	7.573%	$58.5843	$58.58	$58.60	$58.60
Purchase #3	$161.57	7.279%	$173.3307	$173.33	$173.35	$173.30
Purchase #4	$196.29	13.777%	$223.3329	$223.33	$223.35	$223.30
Purchase #5	$207.45	12.610%	$233.6094	$233.61	$233.60	$233.60
Purchase #6	$62.72	4.604%	$65.6076	$65.61	$65.60	$65.60
Purchase #7	$13.87	5.619%	$14.6494	$14.65	$14.65	$14.60
7 purchase totals =	$939.64		$1,040.2304	$1,040.23	$1,040.25	$1,040.10