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	$10.73	13.199%	$12.1463	$12.15	$12.15	$12.10
Purchase #2	$80.95	3.661%	$83.9136	$83.91	$83.90	$83.90
Purchase #3	$24.78	5.549%	$26.155	$26.16	$26.15	$26.20
Purchase #4	$247.52	3.551%	$256.3094	$256.31	$256.30	$256.30
Purchase #5	$25.60	5.527%	$27.0149	$27.01	$27.00	$27.00
Purchase #6	$212.43	10.102%	$233.8897	$233.89	$233.90	$233.90
Purchase #7	$38.41	4.856%	$40.2752	$40.28	$40.30	$40.30
7 purchase totals =	$640.42		$679.7041	$679.71	$679.70	$679.70