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	$12.48	6.575%	$13.3006	$13.30	$13.30	$13.30
Purchase #2	$18.74	11.405%	$20.8773	$20.88	$20.90	$20.90
Purchase #3	$141.66	3.212%	$146.2101	$146.21	$146.20	$146.20
Purchase #4	$66.83	9.733%	$73.3346	$73.33	$73.35	$73.30
Purchase #5	$68.27	4.379%	$71.2595	$71.26	$71.25	$71.30
Purchase #6	$219.72	9.470%	$240.5275	$240.53	$240.55	$240.50
Purchase #7	$63.91	3.827%	$66.3558	$66.36	$66.35	$66.40
7 purchase totals =	$591.61		$631.8654	$631.87	$631.90	$631.90