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	$36.56	4.805%	$38.3167	$38.32	$38.30	$38.30
Purchase #2	$236.48	7.583%	$254.4123	$254.41	$254.40	$254.40
Purchase #3	$111.86	13.486%	$126.9454	$126.95	$126.95	$126.90
Purchase #4	$42.90	6.450%	$45.6671	$45.67	$45.65	$45.70
Purchase #5	$156.87	11.649%	$175.1438	$175.14	$175.15	$175.10
Purchase #6	$98.50	6.873%	$105.2699	$105.27	$105.25	$105.30
Purchase #7	$229.96	13.230%	$260.3837	$260.38	$260.40	$260.40
7 purchase totals =	$913.13		$1,006.1389	$1,006.14	$1,006.10	$1,006.10