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	$141.32	6.343%	$150.2839	$150.28	$150.30	$150.30
Purchase #2	$249.38	12.102%	$279.56	$279.56	$279.55	$279.60
Purchase #3	$53.93	10.182%	$59.4212	$59.42	$59.40	$59.40
Purchase #4	$230.44	3.484%	$238.4685	$238.47	$238.45	$238.50
Purchase #5	$78.78	4.137%	$82.0391	$82.04	$82.05	$82.00
Purchase #6	$13.72	11.209%	$15.2579	$15.26	$15.25	$15.30
Purchase #7	$157.48	9.560%	$172.5351	$172.54	$172.55	$172.50
7 purchase totals =	$925.05		$997.5657	$997.57	$997.55	$997.60