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	$238.58	6.613%	$254.3573	$254.36	$254.35	$254.40
Purchase #2	$247.97	9.194%	$270.7684	$270.77	$270.75	$270.80
Purchase #3	$196.88	12.860%	$222.1988	$222.20	$222.20	$222.20
Purchase #4	$80.39	11.581%	$89.7	$89.70	$89.70	$89.70
Purchase #5	$56.72	4.288%	$59.1522	$59.15	$59.15	$59.20
Purchase #6	$48.58	3.772%	$50.4124	$50.41	$50.40	$50.40
Purchase #7	$27.75	7.221%	$29.7538	$29.75	$29.75	$29.80
7 purchase totals =	$896.87		$976.3429	$976.34	$976.30	$976.50