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	$176.94	5.560%	$186.7779	$186.78	$186.80	$186.80
Purchase #2	$220.51	5.798%	$233.2952	$233.30	$233.30	$233.30
Purchase #3	$150.99	11.175%	$167.8631	$167.86	$167.85	$167.90
Purchase #4	$108.55	13.532%	$123.239	$123.24	$123.25	$123.20
Purchase #5	$29.47	13.350%	$33.4042	$33.40	$33.40	$33.40
Purchase #6	$62.82	12.753%	$70.8314	$70.83	$70.85	$70.80
Purchase #7	$64.47	10.816%	$71.4431	$71.44	$71.45	$71.40
7 purchase totals =	$813.75		$886.8539	$886.85	$886.90	$886.80