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	$40.81	4.440%	$42.622	$42.62	$42.60	$42.60
Purchase #2	$244.94	10.556%	$270.7959	$270.80	$270.80	$270.80
Purchase #3	$26.68	7.262%	$28.6175	$28.62	$28.60	$28.60
Purchase #4	$116.42	12.828%	$131.3544	$131.35	$131.35	$131.40
Purchase #5	$18.52	8.519%	$20.0977	$20.10	$20.10	$20.10
Purchase #6	$169.99	12.637%	$191.4716	$191.47	$191.45	$191.50
Purchase #7	$87.70	13.541%	$99.5755	$99.58	$99.60	$99.60
7 purchase totals =	$705.06		$784.5346	$784.54	$784.50	$784.60