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	$90.30	3.679%	$93.6221	$93.62	$93.60	$93.60
Purchase #2	$161.51	6.178%	$171.4881	$171.49	$171.50	$171.50
Purchase #3	$117.78	11.480%	$131.3011	$131.30	$131.30	$131.30
Purchase #4	$33.71	12.456%	$37.9089	$37.91	$37.90	$37.90
Purchase #5	$16.66	5.663%	$17.6035	$17.60	$17.60	$17.60
Purchase #6	$39.32	3.531%	$40.7084	$40.71	$40.70	$40.70
Purchase #7	$85.61	6.288%	$90.9932	$90.99	$91.00	$91.00
7 purchase totals =	$544.89		$583.6253	$583.62	$583.60	$583.60