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	$33.40	5.792%	$35.3345	$35.33	$35.35	$35.30
Purchase #2	$129.56	9.851%	$142.323	$142.32	$142.30	$142.30
Purchase #3	$44.52	10.800%	$49.3282	$49.33	$49.35	$49.30
Purchase #4	$59.52	8.191%	$64.3953	$64.40	$64.40	$64.40
Purchase #5	$37.89	8.313%	$41.0398	$41.04	$41.05	$41.00
Purchase #6	$34.60	9.849%	$38.0078	$38.01	$38.00	$38.00
Purchase #7	$51.46	10.162%	$56.6894	$56.69	$56.70	$56.70
7 purchase totals =	$390.95		$427.1180	$427.12	$427.15	$427.00