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	$114.69	5.304%	$120.7732	$120.77	$120.75	$120.80
Purchase #2	$229.87	4.525%	$240.2716	$240.27	$240.25	$240.30
Purchase #3	$35.27	12.578%	$39.7063	$39.71	$39.70	$39.70
Purchase #4	$159.39	7.756%	$171.7523	$171.75	$171.75	$171.80
Purchase #5	$242.31	9.827%	$266.1218	$266.12	$266.10	$266.10
Purchase #6	$52.85	13.273%	$59.8648	$59.86	$59.85	$59.90
Purchase #7	$92.25	8.640%	$100.2204	$100.22	$100.20	$100.20
7 purchase totals =	$926.63		$998.7104	$998.70	$998.60	$998.80