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	$47.91	13.871%	$54.5556	$54.56	$54.55	$54.60
Purchase #2	$19.58	6.586%	$20.8695	$20.87	$20.85	$20.90
Purchase #3	$215.91	5.386%	$227.5389	$227.54	$227.55	$227.50
Purchase #4	$195.93	6.728%	$209.1122	$209.11	$209.10	$209.10
Purchase #5	$110.25	7.580%	$118.607	$118.61	$118.60	$118.60
Purchase #6	$49.84	12.487%	$56.0635	$56.06	$56.05	$56.10
Purchase #7	$139.60	8.609%	$151.6182	$151.62	$151.60	$151.60
7 purchase totals =	$779.02		$838.3649	$838.37	$838.30	$838.40