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	$28.30	8.120%	$30.598	$30.60	$30.60	$30.60
Purchase #2	$80.53	12.412%	$90.5254	$90.53	$90.55	$90.50
Purchase #3	$73.86	6.114%	$78.3758	$78.38	$78.40	$78.40
Purchase #4	$112.72	9.202%	$123.0925	$123.09	$123.10	$123.10
Purchase #5	$112.52	10.787%	$124.6575	$124.66	$124.65	$124.70
Purchase #6	$57.62	5.209%	$60.6214	$60.62	$60.60	$60.60
Purchase #7	$31.64	12.381%	$35.5573	$35.56	$35.55	$35.60
7 purchase totals =	$497.19		$543.4279	$543.44	$543.45	$543.50