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	$19.81	5.554%	$20.9102	$20.91	$20.90	$20.90
Purchase #2	$47.41	7.111%	$50.7813	$50.78	$50.80	$50.80
Purchase #3	$54.27	7.426%	$58.3001	$58.30	$58.30	$58.30
Purchase #4	$229.46	12.738%	$258.6886	$258.69	$258.70	$258.70
Purchase #5	$181.85	8.102%	$196.5835	$196.58	$196.60	$196.60
Purchase #6	$12.89	10.426%	$14.2339	$14.23	$14.25	$14.20
Purchase #7	$92.71	10.712%	$102.6411	$102.64	$102.65	$102.60
7 purchase totals =	$638.40		$702.1387	$702.13	$702.20	$702.10