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	$70.56	11.152%	$78.4289	$78.43	$78.45	$78.40
Purchase #2	$55.43	10.734%	$61.3799	$61.38	$61.40	$61.40
Purchase #3	$225.28	4.327%	$235.0279	$235.03	$235.05	$235.00
Purchase #4	$139.50	11.203%	$155.1282	$155.13	$155.15	$155.10
Purchase #5	$75.34	8.712%	$81.9036	$81.90	$81.90	$81.90
Purchase #6	$229.53	7.361%	$246.4257	$246.43	$246.45	$246.40
Purchase #7	$117.40	5.618%	$123.9955	$124.00	$124.00	$124.00
7 purchase totals =	$913.04		$982.2897	$982.30	$982.40	$982.20