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	$79.44	5.189%	$83.5621	$83.56	$83.55	$83.60
Purchase #2	$50.70	8.236%	$54.8757	$54.88	$54.90	$54.90
Purchase #3	$69.39	6.476%	$73.8837	$73.88	$73.90	$73.90
Purchase #4	$167.71	9.245%	$183.2148	$183.21	$183.20	$183.20
Purchase #5	$83.73	11.831%	$93.6361	$93.64	$93.65	$93.60
Purchase #6	$87.90	11.800%	$98.2722	$98.27	$98.25	$98.30
Purchase #7	$50.28	7.528%	$54.0651	$54.07	$54.05	$54.10
7 purchase totals =	$589.15		$641.5097	$641.51	$641.50	$641.60