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	$148.45	11.857%	$166.0517	$166.05	$166.05	$166.10
Purchase #2	$56.67	9.812%	$62.2305	$62.23	$62.25	$62.20
Purchase #3	$157.29	13.385%	$178.3433	$178.34	$178.35	$178.30
Purchase #4	$177.53	7.186%	$190.2873	$190.29	$190.30	$190.30
Purchase #5	$67.29	8.132%	$72.762	$72.76	$72.75	$72.80
Purchase #6	$78.95	5.724%	$83.4691	$83.47	$83.45	$83.50
Purchase #7	$239.29	4.612%	$250.3261	$250.33	$250.35	$250.30
7 purchase totals =	$925.47		$1,003.4700	$1,003.47	$1,003.50	$1,003.50