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	$249.33	6.249%	$264.9106	$264.91	$264.90	$264.90
Purchase #2	$130.96	11.821%	$146.4408	$146.44	$146.45	$146.40
Purchase #3	$142.43	5.723%	$150.5813	$150.58	$150.60	$150.60
Purchase #4	$64.42	8.141%	$69.6644	$69.66	$69.65	$69.70
Purchase #5	$82.83	9.293%	$90.5274	$90.53	$90.55	$90.50
Purchase #6	$48.68	6.472%	$51.8306	$51.83	$51.85	$51.80
Purchase #7	$211.31	6.697%	$225.4614	$225.46	$225.45	$225.50
7 purchase totals =	$929.96		$999.4165	$999.41	$999.45	$999.40