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	$31.99	11.324%	$35.6125	$35.61	$35.60	$35.60
Purchase #2	$59.54	9.358%	$65.1118	$65.11	$65.10	$65.10
Purchase #3	$92.48	7.307%	$99.2375	$99.24	$99.25	$99.20
Purchase #4	$164.25	6.611%	$175.1086	$175.11	$175.10	$175.10
Purchase #5	$110.98	6.607%	$118.3124	$118.31	$118.30	$118.30
Purchase #6	$5.27	10.537%	$5.8253	$5.83	$5.85	$5.80
Purchase #7	$45.26	11.499%	$50.4644	$50.46	$50.45	$50.50
7 purchase totals =	$509.77		$549.6725	$549.67	$549.65	$549.60