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	$20.85	6.808%	$22.2695	$22.27	$22.25	$22.30
Purchase #2	$217.52	7.705%	$234.2799	$234.28	$234.30	$234.30
Purchase #3	$75.77	8.238%	$82.0119	$82.01	$82.00	$82.00
Purchase #4	$64.31	5.525%	$67.8631	$67.86	$67.85	$67.90
Purchase #5	$204.25	11.488%	$227.7142	$227.71	$227.70	$227.70
Purchase #6	$140.55	8.158%	$152.0161	$152.02	$152.00	$152.00
Purchase #7	$17.91	8.267%	$19.3906	$19.39	$19.40	$19.40
7 purchase totals =	$741.16		$805.5453	$805.54	$805.50	$805.60