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	$142.63	6.456%	$151.8382	$151.84	$151.85	$151.80
Purchase #2	$18.89	11.783%	$21.1158	$21.12	$21.10	$21.10
Purchase #3	$170.58	11.407%	$190.0381	$190.04	$190.05	$190.00
Purchase #4	$205.63	9.717%	$225.6111	$225.61	$225.60	$225.60
Purchase #5	$74.65	12.264%	$83.8051	$83.81	$83.80	$83.80
Purchase #6	$77.35	3.606%	$80.1392	$80.14	$80.15	$80.10
Purchase #7	$38.78	6.419%	$41.2693	$41.27	$41.25	$41.30
7 purchase totals =	$728.51		$793.8168	$793.83	$793.80	$793.70