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	$150.38	13.548%	$170.7535	$170.75	$170.75	$170.80
Purchase #2	$31.69	4.504%	$33.1173	$33.12	$33.10	$33.10
Purchase #3	$228.99	11.365%	$255.0147	$255.01	$255.00	$255.00
Purchase #4	$234.64	6.647%	$250.2365	$250.24	$250.25	$250.20
Purchase #5	$166.53	3.399%	$172.1904	$172.19	$172.20	$172.20
Purchase #6	$37.96	8.609%	$41.228	$41.23	$41.25	$41.20
Purchase #7	$113.67	12.135%	$127.4639	$127.46	$127.45	$127.50
7 purchase totals =	$963.86		$1,050.0043	$1,050.00	$1,050.00	$1,050.00