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	$221.57	12.427%	$249.1045	$249.10	$249.10	$249.10
Purchase #2	$58.71	11.418%	$65.4135	$65.41	$65.40	$65.40
Purchase #3	$51.52	6.540%	$54.8894	$54.89	$54.90	$54.90
Purchase #4	$141.66	6.456%	$150.8056	$150.81	$150.80	$150.80
Purchase #5	$85.67	6.142%	$90.9319	$90.93	$90.95	$90.90
Purchase #6	$151.49	11.794%	$169.3567	$169.36	$169.35	$169.40
Purchase #7	$143.38	7.120%	$153.5887	$153.59	$153.60	$153.60
7 purchase totals =	$854.00		$934.0903	$934.09	$934.10	$934.10