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	$243.90	13.735%	$277.3997	$277.40	$277.40	$277.40
Purchase #2	$41.85	7.492%	$44.9854	$44.99	$45.00	$45.00
Purchase #3	$156.80	7.236%	$168.146	$168.15	$168.15	$168.10
Purchase #4	$172.86	10.797%	$191.5237	$191.52	$191.50	$191.50
Purchase #5	$153.39	6.161%	$162.8404	$162.84	$162.85	$162.80
Purchase #6	$196.37	12.127%	$220.1838	$220.18	$220.20	$220.20
Purchase #7	$78.77	3.599%	$81.6049	$81.60	$81.60	$81.60
7 purchase totals =	$1,043.94		$1,146.6839	$1,146.68	$1,146.70	$1,146.60