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	$35.28	8.661%	$38.3356	$38.34	$38.35	$38.30
Purchase #2	$89.68	11.377%	$99.8829	$99.88	$99.90	$99.90
Purchase #3	$124.67	3.361%	$128.8602	$128.86	$128.85	$128.90
Purchase #4	$43.52	4.130%	$45.3174	$45.32	$45.30	$45.30
Purchase #5	$82.77	6.103%	$87.8215	$87.82	$87.80	$87.80
Purchase #6	$27.42	10.582%	$30.3216	$30.32	$30.30	$30.30
Purchase #7	$108.58	9.211%	$118.5813	$118.58	$118.60	$118.60
7 purchase totals =	$511.92		$549.1205	$549.12	$549.10	$549.10