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	$91.42	9.814%	$100.392	$100.39	$100.40	$100.40
Purchase #2	$174.65	7.801%	$188.2744	$188.27	$188.25	$188.30
Purchase #3	$84.49	12.547%	$95.091	$95.09	$95.10	$95.10
Purchase #4	$114.77	5.160%	$120.6921	$120.69	$120.70	$120.70
Purchase #5	$20.82	8.665%	$22.6241	$22.62	$22.60	$22.60
Purchase #6	$113.35	10.202%	$124.914	$124.91	$124.90	$124.90
Purchase #7	$171.91	10.685%	$190.2786	$190.28	$190.30	$190.30
7 purchase totals =	$771.41		$842.2662	$842.25	$842.25	$842.30