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	$53.90	13.809%	$61.3431	$61.34	$61.35	$61.30
Purchase #2	$183.99	6.840%	$196.5749	$196.57	$196.55	$196.60
Purchase #3	$118.77	9.722%	$130.3168	$130.32	$130.30	$130.30
Purchase #4	$154.91	12.114%	$173.6758	$173.68	$173.70	$173.70
Purchase #5	$58.32	5.486%	$61.5194	$61.52	$61.50	$61.50
Purchase #6	$159.54	12.122%	$178.8794	$178.88	$178.90	$178.90
Purchase #7	$34.25	8.731%	$37.2404	$37.24	$37.25	$37.20
7 purchase totals =	$763.68		$839.5498	$839.55	$839.55	$839.50