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	$91.42	8.814%	$99.4778	$99.48	$99.50	$99.50
Purchase #2	$201.53	4.198%	$209.9902	$209.99	$210.00	$210.00
Purchase #3	$129.77	5.144%	$136.4454	$136.45	$136.45	$136.40
Purchase #4	$82.52	8.342%	$89.4038	$89.40	$89.40	$89.40
Purchase #5	$154.95	11.197%	$172.2998	$172.30	$172.30	$172.30
Purchase #6	$54.87	4.190%	$57.1691	$57.17	$57.15	$57.20
Purchase #7	$35.32	8.520%	$38.3293	$38.33	$38.35	$38.30
7 purchase totals =	$750.38		$803.1154	$803.12	$803.15	$803.10