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	$27.78	12.729%	$31.3161	$31.32	$31.30	$31.30
Purchase #2	$234.89	3.153%	$242.2961	$242.30	$242.30	$242.30
Purchase #3	$39.32	3.514%	$40.7017	$40.70	$40.70	$40.70
Purchase #4	$184.34	8.515%	$200.0366	$200.04	$200.05	$200.00
Purchase #5	$147.45	13.682%	$167.6241	$167.62	$167.60	$167.60
Purchase #6	$101.66	4.363%	$106.0954	$106.10	$106.10	$106.10
Purchase #7	$183.60	3.713%	$190.4171	$190.42	$190.40	$190.40
7 purchase totals =	$919.04		$978.4871	$978.50	$978.45	$978.40