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	$155.69	11.428%	$173.4823	$173.48	$173.50	$173.50
Purchase #2	$129.99	12.338%	$146.0282	$146.03	$146.05	$146.00
Purchase #3	$198.73	12.618%	$223.8058	$223.81	$223.80	$223.80
Purchase #4	$102.61	8.794%	$111.6335	$111.63	$111.65	$111.60
Purchase #5	$158.71	3.522%	$164.2998	$164.30	$164.30	$164.30
Purchase #6	$31.75	11.294%	$35.3358	$35.34	$35.35	$35.30
Purchase #7	$56.85	4.277%	$59.2815	$59.28	$59.30	$59.30
7 purchase totals =	$834.33		$913.8669	$913.87	$913.95	$913.80