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	$217.93	12.106%	$244.3126	$244.31	$244.30	$244.30
Purchase #2	$76.69	7.161%	$82.1818	$82.18	$82.20	$82.20
Purchase #3	$204.38	12.103%	$229.1161	$229.12	$229.10	$229.10
Purchase #4	$59.58	10.423%	$65.79	$65.79	$65.80	$65.80
Purchase #5	$156.31	5.654%	$165.1478	$165.15	$165.15	$165.10
Purchase #6	$122.68	3.473%	$126.9407	$126.94	$126.95	$126.90
Purchase #7	$174.66	8.722%	$189.8938	$189.89	$189.90	$189.90
7 purchase totals =	$1,012.23		$1,103.3828	$1,103.38	$1,103.40	$1,103.30