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	$38.49	12.598%	$43.339	$43.34	$43.35	$43.30
Purchase #2	$135.93	3.611%	$140.8384	$140.84	$140.85	$140.80
Purchase #3	$64.39	12.764%	$72.6087	$72.61	$72.60	$72.60
Purchase #4	$49.72	5.352%	$52.381	$52.38	$52.40	$52.40
Purchase #5	$72.59	7.551%	$78.0713	$78.07	$78.05	$78.10
Purchase #6	$60.38	10.340%	$66.6233	$66.62	$66.60	$66.60
Purchase #7	$196.72	11.557%	$219.4549	$219.45	$219.45	$219.50
7 purchase totals =	$618.22		$673.3166	$673.31	$673.30	$673.30