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	$40.90	6.631%	$43.6121	$43.61	$43.60	$43.60
Purchase #2	$20.95	3.611%	$21.7065	$21.71	$21.70	$21.70
Purchase #3	$111.71	11.120%	$124.1322	$124.13	$124.15	$124.10
Purchase #4	$57.81	6.517%	$61.5775	$61.58	$61.60	$61.60
Purchase #5	$64.56	7.716%	$69.5414	$69.54	$69.55	$69.50
Purchase #6	$207.25	10.640%	$229.3014	$229.30	$229.30	$229.30
Purchase #7	$207.49	7.140%	$222.3048	$222.30	$222.30	$222.30
7 purchase totals =	$710.67		$772.1759	$772.17	$772.20	$772.10