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	$37.40	12.777%	$42.1786	$42.18	$42.20	$42.20
Purchase #2	$194.69	10.545%	$215.2201	$215.22	$215.20	$215.20
Purchase #3	$38.72	7.808%	$41.7433	$41.74	$41.75	$41.70
Purchase #4	$203.85	7.846%	$219.8441	$219.84	$219.85	$219.80
Purchase #5	$106.96	11.685%	$119.4583	$119.46	$119.45	$119.50
Purchase #6	$94.29	11.788%	$105.4049	$105.40	$105.40	$105.40
Purchase #7	$159.54	5.395%	$168.1472	$168.15	$168.15	$168.10
7 purchase totals =	$835.45		$911.9965	$911.99	$912.00	$911.90