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	$217.71	6.671%	$232.2334	$232.23	$232.25	$232.20
Purchase #2	$234.47	13.467%	$266.0461	$266.05	$266.05	$266.00
Purchase #3	$89.67	11.436%	$99.9247	$99.92	$99.90	$99.90
Purchase #4	$191.60	4.522%	$200.2642	$200.26	$200.25	$200.30
Purchase #5	$125.88	9.485%	$137.8197	$137.82	$137.80	$137.80
Purchase #6	$134.35	13.533%	$152.5316	$152.53	$152.55	$152.50
Purchase #7	$248.59	12.137%	$278.7614	$278.76	$278.75	$278.80
7 purchase totals =	$1,242.27		$1,367.5811	$1,367.57	$1,367.55	$1,367.50