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	$20.51	6.816%	$21.908	$21.91	$21.90	$21.90
Purchase #2	$100.54	4.854%	$105.4202	$105.42	$105.40	$105.40
Purchase #3	$230.78	9.405%	$252.4849	$252.48	$252.50	$252.50
Purchase #4	$61.64	9.190%	$67.3047	$67.30	$67.30	$67.30
Purchase #5	$40.99	6.506%	$43.6568	$43.66	$43.65	$43.70
Purchase #6	$13.27	4.635%	$13.8851	$13.89	$13.90	$13.90
Purchase #7	$88.61	3.136%	$91.3888	$91.39	$91.40	$91.40
7 purchase totals =	$556.34		$596.0485	$596.05	$596.05	$596.10