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	$75.80	7.561%	$81.5312	$81.53	$81.55	$81.50
Purchase #2	$112.43	9.322%	$122.9107	$122.91	$122.90	$122.90
Purchase #3	$250.87	5.863%	$265.5785	$265.58	$265.60	$265.60
Purchase #4	$64.92	9.163%	$70.8686	$70.87	$70.85	$70.90
Purchase #5	$90.85	10.187%	$100.1049	$100.10	$100.10	$100.10
Purchase #6	$57.83	13.179%	$65.4514	$65.45	$65.45	$65.50
Purchase #7	$94.98	9.563%	$104.0629	$104.06	$104.05	$104.10
7 purchase totals =	$747.68		$810.5082	$810.50	$810.50	$810.60