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	$37.37	5.116%	$39.2818	$39.28	$39.30	$39.30
Purchase #2	$145.27	9.686%	$159.3409	$159.34	$159.35	$159.30
Purchase #3	$37.29	6.814%	$39.8309	$39.83	$39.85	$39.80
Purchase #4	$214.31	3.825%	$222.5074	$222.51	$222.50	$222.50
Purchase #5	$71.34	8.578%	$77.4595	$77.46	$77.45	$77.50
Purchase #6	$94.32	9.518%	$103.2974	$103.30	$103.30	$103.30
Purchase #7	$116.92	9.248%	$127.7328	$127.73	$127.75	$127.70
7 purchase totals =	$716.82		$769.4507	$769.45	$769.50	$769.40