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	$242.58	10.252%	$267.4493	$267.45	$267.45	$267.40
Purchase #2	$94.55	8.433%	$102.5234	$102.52	$102.50	$102.50
Purchase #3	$226.35	9.387%	$247.5975	$247.60	$247.60	$247.60
Purchase #4	$71.75	7.592%	$77.1973	$77.20	$77.20	$77.20
Purchase #5	$70.81	10.784%	$78.4462	$78.45	$78.45	$78.40
Purchase #6	$220.35	13.674%	$250.4807	$250.48	$250.50	$250.50
Purchase #7	$222.36	12.783%	$250.7843	$250.78	$250.80	$250.80
7 purchase totals =	$1,148.75		$1,274.4787	$1,274.48	$1,274.50	$1,274.40