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	$91.41	9.776%	$100.3462	$100.35	$100.35	$100.30
Purchase #2	$74.57	10.861%	$82.669	$82.67	$82.65	$82.70
Purchase #3	$77.78	12.774%	$87.7156	$87.72	$87.70	$87.70
Purchase #4	$149.89	7.157%	$160.6176	$160.62	$160.60	$160.60
Purchase #5	$44.71	13.574%	$50.7789	$50.78	$50.80	$50.80
Purchase #6	$194.26	12.679%	$218.8902	$218.89	$218.90	$218.90
Purchase #7	$71.85	7.531%	$77.261	$77.26	$77.25	$77.30
7 purchase totals =	$704.47		$778.2785	$778.29	$778.25	$778.30