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	$244.98	13.535%	$278.138	$278.14	$278.15	$278.10
Purchase #2	$58.91	10.853%	$65.3035	$65.30	$65.30	$65.30
Purchase #3	$57.57	3.527%	$59.6005	$59.60	$59.60	$59.60
Purchase #4	$199.78	4.534%	$208.838	$208.84	$208.85	$208.80
Purchase #5	$78.66	13.460%	$89.2476	$89.25	$89.25	$89.20
Purchase #6	$25.95	10.660%	$28.7163	$28.72	$28.70	$28.70
Purchase #7	$6.49	9.660%	$7.1169	$7.12	$7.10	$7.10
7 purchase totals =	$672.34		$736.9608	$736.97	$736.95	$736.80