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	$221.98	11.342%	$247.157	$247.16	$247.15	$247.20
Purchase #2	$96.77	4.309%	$100.9398	$100.94	$100.95	$100.90
Purchase #3	$226.79	11.739%	$253.4129	$253.41	$253.40	$253.40
Purchase #4	$130.29	6.857%	$139.224	$139.22	$139.20	$139.20
Purchase #5	$7.29	8.762%	$7.9287	$7.93	$7.95	$7.90
Purchase #6	$20.50	11.571%	$22.8721	$22.87	$22.85	$22.90
Purchase #7	$153.72	9.175%	$167.8238	$167.82	$167.80	$167.80
7 purchase totals =	$857.34		$939.3583	$939.35	$939.30	$939.30