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	$28.25	5.851%	$29.9029	$29.90	$29.90	$29.90
Purchase #2	$165.81	5.703%	$175.2661	$175.27	$175.25	$175.30
Purchase #3	$246.29	13.486%	$279.5047	$279.50	$279.50	$279.50
Purchase #4	$179.79	13.618%	$204.2738	$204.27	$204.25	$204.30
Purchase #5	$103.38	13.648%	$117.4893	$117.49	$117.50	$117.50
Purchase #6	$139.72	4.598%	$146.1443	$146.14	$146.15	$146.10
Purchase #7	$57.89	3.372%	$59.8421	$59.84	$59.85	$59.80
7 purchase totals =	$921.13		$1,012.4232	$1,012.41	$1,012.40	$1,012.40