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	$20.69	5.291%	$21.7847	$21.78	$21.80	$21.80
Purchase #2	$138.71	12.505%	$156.0557	$156.06	$156.05	$156.10
Purchase #3	$186.92	9.764%	$205.1709	$205.17	$205.15	$205.20
Purchase #4	$52.57	4.333%	$54.8479	$54.85	$54.85	$54.80
Purchase #5	$115.33	7.194%	$123.6268	$123.63	$123.65	$123.60
Purchase #6	$130.36	6.371%	$138.6652	$138.67	$138.65	$138.70
Purchase #7	$59.72	8.532%	$64.8153	$64.82	$64.80	$64.80
7 purchase totals =	$704.30		$764.9665	$764.98	$764.95	$765.00