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	$14.65	3.186%	$15.1167	$15.12	$15.10	$15.10
Purchase #2	$137.67	9.598%	$150.8836	$150.88	$150.90	$150.90
Purchase #3	$99.27	5.804%	$105.0316	$105.03	$105.05	$105.00
Purchase #4	$57.81	13.451%	$65.586	$65.59	$65.60	$65.60
Purchase #5	$246.91	7.126%	$264.5048	$264.50	$264.50	$264.50
Purchase #6	$39.31	8.116%	$42.5004	$42.50	$42.50	$42.50
Purchase #7	$144.69	10.681%	$160.1443	$160.14	$160.15	$160.10
7 purchase totals =	$740.31		$803.7674	$803.76	$803.80	$803.70