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	$173.85	3.467%	$179.8774	$179.88	$179.90	$179.90
Purchase #2	$171.61	7.167%	$183.9093	$183.91	$183.90	$183.90
Purchase #3	$130.45	5.606%	$137.763	$137.76	$137.75	$137.80
Purchase #4	$242.69	12.420%	$272.8321	$272.83	$272.85	$272.80
Purchase #5	$212.71	8.799%	$231.4264	$231.43	$231.45	$231.40
Purchase #6	$245.89	12.624%	$276.9312	$276.93	$276.95	$276.90
Purchase #7	$95.38	5.453%	$100.5811	$100.58	$100.60	$100.60
7 purchase totals =	$1,272.58		$1,383.3205	$1,383.32	$1,383.40	$1,383.30