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	$116.84	10.686%	$129.3255	$129.33	$129.35	$129.30
Purchase #2	$25.92	8.430%	$28.1051	$28.11	$28.10	$28.10
Purchase #3	$123.45	3.714%	$128.0349	$128.03	$128.05	$128.00
Purchase #4	$111.50	10.463%	$123.1662	$123.17	$123.15	$123.20
Purchase #5	$65.97	10.495%	$72.8936	$72.89	$72.90	$72.90
Purchase #6	$25.76	11.345%	$28.6825	$28.68	$28.70	$28.70
Purchase #7	$147.75	6.267%	$157.0095	$157.01	$157.00	$157.00
7 purchase totals =	$617.19		$667.2173	$667.22	$667.25	$667.20