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	$79.36	11.714%	$88.6562	$88.66	$88.65	$88.70
Purchase #2	$34.60	11.380%	$38.5375	$38.54	$38.55	$38.50
Purchase #3	$60.89	8.159%	$65.858	$65.86	$65.85	$65.90
Purchase #4	$59.66	12.379%	$67.0453	$67.05	$67.05	$67.00
Purchase #5	$230.54	8.492%	$250.1175	$250.12	$250.10	$250.10
Purchase #6	$223.44	9.609%	$244.9103	$244.91	$244.90	$244.90
Purchase #7	$17.34	12.341%	$19.4799	$19.48	$19.50	$19.50
7 purchase totals =	$705.83		$774.6047	$774.62	$774.60	$774.60