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	$52.59	3.806%	$54.5916	$54.59	$54.60	$54.60
Purchase #2	$245.93	13.483%	$279.0887	$279.09	$279.10	$279.10
Purchase #3	$30.85	4.561%	$32.2571	$32.26	$32.25	$32.30
Purchase #4	$129.32	12.409%	$145.3673	$145.37	$145.35	$145.40
Purchase #5	$151.70	3.718%	$157.3402	$157.34	$157.35	$157.30
Purchase #6	$80.64	3.615%	$83.5551	$83.56	$83.55	$83.60
Purchase #7	$130.89	6.399%	$139.2657	$139.27	$139.25	$139.30
7 purchase totals =	$821.92		$891.4657	$891.48	$891.45	$891.60