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	$21.49	6.430%	$22.8718	$22.87	$22.85	$22.90
Purchase #2	$123.50	3.844%	$128.2473	$128.25	$128.25	$128.20
Purchase #3	$94.37	12.803%	$106.4522	$106.45	$106.45	$106.50
Purchase #4	$54.34	10.161%	$59.8615	$59.86	$59.85	$59.90
Purchase #5	$57.79	12.344%	$64.9236	$64.92	$64.90	$64.90
Purchase #6	$235.60	8.397%	$255.3833	$255.38	$255.40	$255.40
Purchase #7	$58.91	4.329%	$61.4602	$61.46	$61.45	$61.50
7 purchase totals =	$646.00		$699.1999	$699.19	$699.15	$699.30