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	$86.44	4.662%	$90.4698	$90.47	$90.45	$90.50
Purchase #2	$91.77	9.110%	$100.1302	$100.13	$100.15	$100.10
Purchase #3	$77.93	8.612%	$84.6413	$84.64	$84.65	$84.60
Purchase #4	$42.87	9.658%	$47.0104	$47.01	$47.00	$47.00
Purchase #5	$91.84	9.356%	$100.4326	$100.43	$100.45	$100.40
Purchase #6	$225.91	12.757%	$254.7293	$254.73	$254.75	$254.70
Purchase #7	$137.76	3.743%	$142.9164	$142.92	$142.90	$142.90
7 purchase totals =	$754.52		$820.3300	$820.33	$820.35	$820.20