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	$215.75	10.537%	$238.4836	$238.48	$238.50	$238.50
Purchase #2	$170.90	10.235%	$188.3916	$188.39	$188.40	$188.40
Purchase #3	$17.37	4.405%	$18.1351	$18.14	$18.15	$18.10
Purchase #4	$92.66	11.199%	$103.037	$103.04	$103.05	$103.00
Purchase #5	$127.63	11.733%	$142.6048	$142.60	$142.60	$142.60
Purchase #6	$241.36	3.754%	$250.4207	$250.42	$250.40	$250.40
Purchase #7	$52.65	7.273%	$56.4792	$56.48	$56.50	$56.50
7 purchase totals =	$918.32		$997.5520	$997.55	$997.60	$997.50