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	$121.32	5.428%	$127.9052	$127.91	$127.90	$127.90
Purchase #2	$107.70	3.317%	$111.2724	$111.27	$111.25	$111.30
Purchase #3	$227.70	5.161%	$239.4516	$239.45	$239.45	$239.50
Purchase #4	$124.46	13.814%	$141.6529	$141.65	$141.65	$141.70
Purchase #5	$154.48	4.707%	$161.7514	$161.75	$161.75	$161.80
Purchase #6	$47.83	12.412%	$53.7667	$53.77	$53.75	$53.80
Purchase #7	$243.93	4.222%	$254.2287	$254.23	$254.25	$254.20
7 purchase totals =	$1,027.42		$1,090.0289	$1,090.03	$1,090.00	$1,090.20