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	$97.37	4.341%	$101.5968	$101.60	$101.60	$101.60
Purchase #2	$63.91	13.872%	$72.7756	$72.78	$72.80	$72.80
Purchase #3	$133.83	13.794%	$152.2905	$152.29	$152.30	$152.30
Purchase #4	$73.72	13.752%	$83.858	$83.86	$83.85	$83.90
Purchase #5	$15.57	9.239%	$17.0085	$17.01	$17.00	$17.00
Purchase #6	$223.89	9.297%	$244.7051	$244.71	$244.70	$244.70
Purchase #7	$155.88	3.791%	$161.7894	$161.79	$161.80	$161.80
7 purchase totals =	$764.17		$834.0239	$834.04	$834.05	$834.10