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	$235.44	5.510%	$248.4127	$248.41	$248.40	$248.40
Purchase #2	$47.64	13.796%	$54.2124	$54.21	$54.20	$54.20
Purchase #3	$238.46	7.224%	$255.6864	$255.69	$255.70	$255.70
Purchase #4	$220.72	5.748%	$233.407	$233.41	$233.40	$233.40
Purchase #5	$76.45	5.259%	$80.4705	$80.47	$80.45	$80.50
Purchase #6	$155.89	6.399%	$165.8654	$165.87	$165.85	$165.90
Purchase #7	$213.59	12.690%	$240.6946	$240.69	$240.70	$240.70
7 purchase totals =	$1,188.19		$1,278.7490	$1,278.75	$1,278.70	$1,278.80