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	$34.86	11.467%	$38.8574	$38.86	$38.85	$38.90
Purchase #2	$119.28	7.569%	$128.3083	$128.31	$128.30	$128.30
Purchase #3	$80.47	11.341%	$89.5961	$89.60	$89.60	$89.60
Purchase #4	$25.79	5.428%	$27.1899	$27.19	$27.20	$27.20
Purchase #5	$88.54	7.380%	$95.0743	$95.07	$95.05	$95.10
Purchase #6	$27.63	4.409%	$28.8482	$28.85	$28.85	$28.80
Purchase #7	$43.61	9.461%	$47.7359	$47.74	$47.75	$47.70
7 purchase totals =	$420.18		$455.6101	$455.62	$455.60	$455.60