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	$130.53	12.505%	$146.8528	$146.85	$146.85	$146.90
Purchase #2	$98.50	5.439%	$103.8574	$103.86	$103.85	$103.90
Purchase #3	$49.72	11.284%	$55.3304	$55.33	$55.35	$55.30
Purchase #4	$205.69	6.119%	$218.2762	$218.28	$218.30	$218.30
Purchase #5	$52.27	4.336%	$54.5364	$54.54	$54.55	$54.50
Purchase #6	$7.34	5.569%	$7.7488	$7.75	$7.75	$7.70
Purchase #7	$16.53	4.174%	$17.22	$17.22	$17.20	$17.20
7 purchase totals =	$560.58		$603.8220	$603.83	$603.85	$603.80