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	$49.66	11.549%	$55.3952	$55.40	$55.40	$55.40
Purchase #2	$103.68	7.157%	$111.1004	$111.10	$111.10	$111.10
Purchase #3	$159.38	12.379%	$179.1097	$179.11	$179.10	$179.10
Purchase #4	$71.52	5.349%	$75.3456	$75.35	$75.35	$75.30
Purchase #5	$153.33	7.347%	$164.5952	$164.60	$164.60	$164.60
Purchase #6	$139.65	11.669%	$155.9458	$155.95	$155.95	$155.90
Purchase #7	$93.69	10.214%	$103.2595	$103.26	$103.25	$103.30
7 purchase totals =	$770.91		$844.7514	$844.77	$844.75	$844.70