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	$79.43	12.834%	$89.624	$89.62	$89.60	$89.60
Purchase #2	$220.26	12.845%	$248.5524	$248.55	$248.55	$248.60
Purchase #3	$12.45	6.166%	$13.2177	$13.22	$13.20	$13.20
Purchase #4	$198.85	5.668%	$210.1208	$210.12	$210.10	$210.10
Purchase #5	$92.45	8.756%	$100.5449	$100.54	$100.55	$100.50
Purchase #6	$155.31	9.465%	$170.0101	$170.01	$170.00	$170.00
Purchase #7	$73.99	5.272%	$77.8908	$77.89	$77.90	$77.90
7 purchase totals =	$832.74		$909.9607	$909.95	$909.90	$909.90