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	$175.84	7.504%	$189.035	$189.04	$189.05	$189.00
Purchase #2	$243.61	7.678%	$262.3144	$262.31	$262.30	$262.30
Purchase #3	$72.72	4.504%	$75.9953	$76.00	$76.00	$76.00
Purchase #4	$81.76	9.196%	$89.2786	$89.28	$89.30	$89.30
Purchase #5	$125.59	9.548%	$137.5813	$137.58	$137.60	$137.60
Purchase #6	$26.53	3.297%	$27.4047	$27.40	$27.40	$27.40
Purchase #7	$78.97	10.428%	$87.205	$87.21	$87.20	$87.20
7 purchase totals =	$805.02		$868.8143	$868.82	$868.85	$868.80