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	$90.43	11.513%	$100.8412	$100.84	$100.85	$100.80
Purchase #2	$107.73	7.546%	$115.8593	$115.86	$115.85	$115.90
Purchase #3	$84.35	7.726%	$90.8669	$90.87	$90.85	$90.90
Purchase #4	$134.62	7.611%	$144.8659	$144.87	$144.85	$144.90
Purchase #5	$120.96	5.366%	$127.4507	$127.45	$127.45	$127.50
Purchase #6	$198.28	9.128%	$216.379	$216.38	$216.40	$216.40
Purchase #7	$242.82	7.166%	$260.2205	$260.22	$260.20	$260.20
7 purchase totals =	$979.19		$1,056.4835	$1,056.49	$1,056.45	$1,056.60