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	$95.85	4.610%	$100.2687	$100.27	$100.25	$100.30
Purchase #2	$158.66	8.602%	$172.3079	$172.31	$172.30	$172.30
Purchase #3	$78.83	13.457%	$89.4382	$89.44	$89.45	$89.40
Purchase #4	$122.36	3.124%	$126.1825	$126.18	$126.20	$126.20
Purchase #5	$166.49	11.282%	$185.2734	$185.27	$185.25	$185.30
Purchase #6	$92.52	4.280%	$96.4799	$96.48	$96.50	$96.50
Purchase #7	$5.94	6.478%	$6.3248	$6.32	$6.30	$6.30
7 purchase totals =	$720.65		$776.2754	$776.27	$776.25	$776.30