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	$63.60	10.174%	$70.0707	$70.07	$70.05	$70.10
Purchase #2	$104.58	11.766%	$116.8849	$116.88	$116.90	$116.90
Purchase #3	$180.68	3.203%	$186.4672	$186.47	$186.45	$186.50
Purchase #4	$218.90	3.303%	$226.1303	$226.13	$226.15	$226.10
Purchase #5	$37.76	4.436%	$39.435	$39.44	$39.45	$39.40
Purchase #6	$152.91	5.106%	$160.7176	$160.72	$160.70	$160.70
Purchase #7	$85.85	4.774%	$89.9485	$89.95	$89.95	$89.90
7 purchase totals =	$844.28		$889.6542	$889.66	$889.65	$889.60