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	$129.61	12.141%	$145.346	$145.35	$145.35	$145.30
Purchase #2	$102.57	12.821%	$115.7205	$115.72	$115.70	$115.70
Purchase #3	$81.31	10.858%	$90.1386	$90.14	$90.15	$90.10
Purchase #4	$220.30	8.267%	$238.5122	$238.51	$238.50	$238.50
Purchase #5	$221.61	4.234%	$230.993	$230.99	$231.00	$231.00
Purchase #6	$31.87	12.111%	$35.7298	$35.73	$35.75	$35.70
Purchase #7	$114.54	4.609%	$119.8191	$119.82	$119.80	$119.80
7 purchase totals =	$901.81		$976.2592	$976.26	$976.25	$976.10