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	$230.76	9.674%	$253.0837	$253.08	$253.10	$253.10
Purchase #2	$102.41	9.171%	$111.802	$111.80	$111.80	$111.80
Purchase #3	$245.77	3.585%	$254.5809	$254.58	$254.60	$254.60
Purchase #4	$66.81	12.124%	$74.91	$74.91	$74.90	$74.90
Purchase #5	$180.96	11.354%	$201.5062	$201.51	$201.50	$201.50
Purchase #6	$25.60	12.863%	$28.8929	$28.89	$28.90	$28.90
Purchase #7	$57.45	4.167%	$59.8439	$59.84	$59.85	$59.80
7 purchase totals =	$909.76		$984.6196	$984.61	$984.65	$984.60