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	$113.27	12.440%	$127.3608	$127.36	$127.35	$127.40
Purchase #2	$84.39	7.239%	$90.499	$90.50	$90.50	$90.50
Purchase #3	$138.37	9.793%	$151.9206	$151.92	$151.90	$151.90
Purchase #4	$143.60	8.664%	$156.0415	$156.04	$156.05	$156.00
Purchase #5	$77.53	4.174%	$80.7661	$80.77	$80.75	$80.80
Purchase #6	$79.40	11.836%	$88.7978	$88.80	$88.80	$88.80
Purchase #7	$180.61	12.103%	$202.4692	$202.47	$202.45	$202.50
7 purchase totals =	$817.17		$897.8550	$897.86	$897.80	$897.90