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	$76.90	11.172%	$85.4913	$85.49	$85.50	$85.50
Purchase #2	$37.36	4.749%	$39.1342	$39.13	$39.15	$39.10
Purchase #3	$236.55	5.759%	$250.1729	$250.17	$250.15	$250.20
Purchase #4	$176.40	11.111%	$195.9998	$196.00	$196.00	$196.00
Purchase #5	$21.74	11.677%	$24.2786	$24.28	$24.30	$24.30
Purchase #6	$19.72	5.604%	$20.8251	$20.83	$20.85	$20.80
Purchase #7	$15.34	7.545%	$16.4974	$16.50	$16.50	$16.50
7 purchase totals =	$584.01		$632.3993	$632.40	$632.45	$632.40