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	$112.52	12.195%	$126.2418	$126.24	$126.25	$126.20
Purchase #2	$99.57	12.217%	$111.7345	$111.73	$111.75	$111.70
Purchase #3	$240.74	13.113%	$272.3082	$272.31	$272.30	$272.30
Purchase #4	$84.31	3.508%	$87.2676	$87.27	$87.25	$87.30
Purchase #5	$66.71	11.444%	$74.3443	$74.34	$74.35	$74.30
Purchase #6	$137.76	9.208%	$150.4449	$150.44	$150.45	$150.40
Purchase #7	$94.72	5.357%	$99.7942	$99.79	$99.80	$99.80
7 purchase totals =	$836.33		$922.1355	$922.12	$922.15	$922.00