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	$250.56	12.179%	$281.0757	$281.08	$281.10	$281.10
Purchase #2	$35.64	5.255%	$37.5129	$37.51	$37.50	$37.50
Purchase #3	$155.78	12.577%	$175.3725	$175.37	$175.35	$175.40
Purchase #4	$116.35	4.720%	$121.8417	$121.84	$121.85	$121.80
Purchase #5	$150.27	12.325%	$168.7908	$168.79	$168.80	$168.80
Purchase #6	$61.72	12.667%	$69.5381	$69.54	$69.55	$69.50
Purchase #7	$136.85	5.468%	$144.333	$144.33	$144.35	$144.30
7 purchase totals =	$907.17		$998.4647	$998.46	$998.50	$998.40