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	$16.58	9.428%	$18.1432	$18.14	$18.15	$18.10
Purchase #2	$38.52	3.167%	$39.7399	$39.74	$39.75	$39.70
Purchase #3	$80.58	11.547%	$89.8846	$89.88	$89.90	$89.90
Purchase #4	$19.92	12.790%	$22.4678	$22.47	$22.45	$22.50
Purchase #5	$129.67	6.164%	$137.6629	$137.66	$137.65	$137.70
Purchase #6	$77.49	9.872%	$85.1398	$85.14	$85.15	$85.10
Purchase #7	$119.97	6.684%	$127.9888	$127.99	$128.00	$128.00
7 purchase totals =	$482.73		$521.0270	$521.02	$521.05	$521.00