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	$29.66	3.833%	$30.7969	$30.80	$30.80	$30.80
Purchase #2	$97.61	3.120%	$100.6554	$100.66	$100.65	$100.70
Purchase #3	$202.39	10.336%	$223.309	$223.31	$223.30	$223.30
Purchase #4	$93.25	11.142%	$103.6399	$103.64	$103.65	$103.60
Purchase #5	$118.58	7.793%	$127.8209	$127.82	$127.80	$127.80
Purchase #6	$242.46	5.733%	$256.3602	$256.36	$256.35	$256.40
Purchase #7	$59.78	6.317%	$63.5563	$63.56	$63.55	$63.60
7 purchase totals =	$843.73		$906.1386	$906.15	$906.10	$906.20