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	$78.38	5.145%	$82.4127	$82.41	$82.40	$82.40
Purchase #2	$188.65	11.167%	$209.7165	$209.72	$209.70	$209.70
Purchase #3	$191.85	12.254%	$215.3593	$215.36	$215.35	$215.40
Purchase #4	$40.45	4.144%	$42.1262	$42.13	$42.15	$42.10
Purchase #5	$67.60	11.136%	$75.1279	$75.13	$75.15	$75.10
Purchase #6	$155.41	7.351%	$166.8342	$166.83	$166.85	$166.80
Purchase #7	$10.72	10.610%	$11.8574	$11.86	$11.85	$11.90
7 purchase totals =	$733.06		$803.4342	$803.44	$803.45	$803.40