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	$240.31	12.601%	$270.5915	$270.59	$270.60	$270.60
Purchase #2	$179.60	9.539%	$196.732	$196.73	$196.75	$196.70
Purchase #3	$234.26	7.754%	$252.4245	$252.42	$252.40	$252.40
Purchase #4	$246.96	4.535%	$258.1596	$258.16	$258.15	$258.20
Purchase #5	$211.61	6.112%	$224.5436	$224.54	$224.55	$224.50
Purchase #6	$92.52	13.614%	$105.1157	$105.12	$105.10	$105.10
Purchase #7	$215.89	3.649%	$223.7678	$223.77	$223.75	$223.80
7 purchase totals =	$1,421.15		$1,531.3347	$1,531.33	$1,531.30	$1,531.30