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	$84.93	6.296%	$90.2772	$90.28	$90.30	$90.30
Purchase #2	$247.91	5.133%	$260.6352	$260.64	$260.65	$260.60
Purchase #3	$5.78	10.834%	$6.4062	$6.41	$6.40	$6.40
Purchase #4	$7.46	13.174%	$8.4428	$8.44	$8.45	$8.40
Purchase #5	$55.61	8.480%	$60.3257	$60.33	$60.35	$60.30
Purchase #6	$84.85	5.562%	$89.5694	$89.57	$89.55	$89.60
Purchase #7	$214.99	3.470%	$222.4502	$222.45	$222.45	$222.50
7 purchase totals =	$701.53		$738.1067	$738.12	$738.15	$738.10