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	$39.29	3.250%	$40.5669	$40.57	$40.55	$40.60
Purchase #2	$133.81	12.590%	$150.6567	$150.66	$150.65	$150.70
Purchase #3	$222.26	5.450%	$234.3732	$234.37	$234.35	$234.40
Purchase #4	$106.63	6.342%	$113.3925	$113.39	$113.40	$113.40
Purchase #5	$87.49	13.737%	$99.5085	$99.51	$99.50	$99.50
Purchase #6	$116.91	11.633%	$130.5101	$130.51	$130.50	$130.50
Purchase #7	$113.55	8.541%	$123.2483	$123.25	$123.25	$123.20
7 purchase totals =	$819.94		$892.2562	$892.26	$892.20	$892.30