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	$99.31	3.845%	$103.1285	$103.13	$103.15	$103.10
Purchase #2	$184.27	10.382%	$203.4009	$203.40	$203.40	$203.40
Purchase #3	$74.42	5.561%	$78.5585	$78.56	$78.55	$78.60
Purchase #4	$147.52	6.134%	$156.5689	$156.57	$156.55	$156.60
Purchase #5	$91.43	7.233%	$98.0431	$98.04	$98.05	$98.00
Purchase #6	$80.65	13.117%	$91.2289	$91.23	$91.25	$91.20
Purchase #7	$147.99	7.296%	$158.7874	$158.79	$158.80	$158.80
7 purchase totals =	$825.59		$889.7162	$889.72	$889.75	$889.70