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	$83.92	8.128%	$90.741	$90.74	$90.75	$90.70
Purchase #2	$80.39	12.496%	$90.4355	$90.44	$90.45	$90.40
Purchase #3	$139.30	5.206%	$146.552	$146.55	$146.55	$146.60
Purchase #4	$136.53	12.405%	$153.4665	$153.47	$153.45	$153.50
Purchase #5	$139.31	10.393%	$153.7885	$153.79	$153.80	$153.80
Purchase #6	$116.64	11.132%	$129.6244	$129.62	$129.60	$129.60
Purchase #7	$211.74	7.606%	$227.8449	$227.84	$227.85	$227.80
7 purchase totals =	$907.83		$992.4528	$992.45	$992.45	$992.40