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	$40.54	13.828%	$46.1459	$46.15	$46.15	$46.10
Purchase #2	$47.81	11.184%	$53.1571	$53.16	$53.15	$53.20
Purchase #3	$98.51	4.711%	$103.1508	$103.15	$103.15	$103.20
Purchase #4	$179.69	7.604%	$193.3536	$193.35	$193.35	$193.40
Purchase #5	$244.88	3.325%	$253.0223	$253.02	$253.00	$253.00
Purchase #6	$114.47	11.689%	$127.8504	$127.85	$127.85	$127.90
Purchase #7	$162.39	10.581%	$179.5725	$179.57	$179.55	$179.60
7 purchase totals =	$888.29		$956.2526	$956.25	$956.20	$956.40