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	$144.86	9.185%	$158.1654	$158.17	$158.15	$158.20
Purchase #2	$49.31	5.830%	$52.1848	$52.18	$52.20	$52.20
Purchase #3	$176.32	13.437%	$200.0121	$200.01	$200.00	$200.00
Purchase #4	$85.49	12.596%	$96.2583	$96.26	$96.25	$96.30
Purchase #5	$53.71	11.154%	$59.7008	$59.70	$59.70	$59.70
Purchase #6	$95.43	4.306%	$99.5392	$99.54	$99.55	$99.50
Purchase #7	$160.78	4.438%	$167.9154	$167.92	$167.90	$167.90
7 purchase totals =	$765.90		$833.7760	$833.78	$833.75	$833.80