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	$132.41	7.104%	$141.8164	$141.82	$141.80	$141.80
Purchase #2	$35.63	9.807%	$39.1242	$39.12	$39.10	$39.10
Purchase #3	$72.61	8.354%	$78.6758	$78.68	$78.70	$78.70
Purchase #4	$64.64	3.112%	$66.6516	$66.65	$66.65	$66.70
Purchase #5	$107.43	3.309%	$110.9849	$110.98	$111.00	$111.00
Purchase #6	$19.50	7.297%	$20.9229	$20.92	$20.90	$20.90
Purchase #7	$158.58	7.384%	$170.2895	$170.29	$170.30	$170.30
7 purchase totals =	$590.80		$628.4653	$628.46	$628.45	$628.50