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	$5.55	4.731%	$5.8126	$5.81	$5.80	$5.80
Purchase #2	$99.48	11.675%	$111.0943	$111.09	$111.10	$111.10
Purchase #3	$170.37	10.554%	$188.3508	$188.35	$188.35	$188.40
Purchase #4	$35.76	7.544%	$38.4577	$38.46	$38.45	$38.50
Purchase #5	$130.93	8.135%	$141.5812	$141.58	$141.60	$141.60
Purchase #6	$89.86	6.757%	$95.9318	$95.93	$95.95	$95.90
Purchase #7	$225.69	6.530%	$240.4276	$240.43	$240.45	$240.40
7 purchase totals =	$757.64		$821.6560	$821.65	$821.70	$821.70