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	$167.55	11.540%	$186.8853	$186.89	$186.90	$186.90
Purchase #2	$140.43	6.218%	$149.1619	$149.16	$149.15	$149.20
Purchase #3	$180.52	8.808%	$196.4202	$196.42	$196.40	$196.40
Purchase #4	$47.93	4.871%	$50.2647	$50.26	$50.25	$50.30
Purchase #5	$115.68	7.404%	$124.2449	$124.24	$124.25	$124.20
Purchase #6	$42.79	13.316%	$48.4879	$48.49	$48.50	$48.50
Purchase #7	$124.69	7.351%	$133.856	$133.86	$133.85	$133.90
7 purchase totals =	$819.59		$889.3209	$889.32	$889.30	$889.40