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	$137.87	6.268%	$146.5117	$146.51	$146.50	$146.50
Purchase #2	$92.71	7.462%	$99.628	$99.63	$99.65	$99.60
Purchase #3	$59.69	10.652%	$66.0482	$66.05	$66.05	$66.00
Purchase #4	$99.28	4.184%	$103.4339	$103.43	$103.45	$103.40
Purchase #5	$132.65	7.471%	$142.5603	$142.56	$142.55	$142.60
Purchase #6	$132.95	8.633%	$144.4276	$144.43	$144.45	$144.40
Purchase #7	$86.61	10.696%	$95.8738	$95.87	$95.85	$95.90
7 purchase totals =	$741.76		$798.4835	$798.48	$798.50	$798.40