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	$30.99	7.348%	$33.2671	$33.27	$33.25	$33.30
Purchase #2	$185.30	11.606%	$206.8059	$206.81	$206.80	$206.80
Purchase #3	$190.34	10.793%	$210.8834	$210.88	$210.90	$210.90
Purchase #4	$178.26	11.635%	$199.0006	$199.00	$199.00	$199.00
Purchase #5	$52.43	13.651%	$59.5872	$59.59	$59.60	$59.60
Purchase #6	$222.68	11.629%	$248.5755	$248.58	$248.60	$248.60
Purchase #7	$35.87	4.245%	$37.3927	$37.39	$37.40	$37.40
7 purchase totals =	$895.87		$995.5124	$995.52	$995.55	$995.60