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	$123.53	10.435%	$136.4204	$136.42	$136.40	$136.40
Purchase #2	$181.35	12.484%	$203.9897	$203.99	$204.00	$204.00
Purchase #3	$61.50	13.535%	$69.824	$69.82	$69.80	$69.80
Purchase #4	$72.37	13.733%	$82.3086	$82.31	$82.30	$82.30
Purchase #5	$54.78	5.178%	$57.6165	$57.62	$57.60	$57.60
Purchase #6	$35.94	13.571%	$40.8174	$40.82	$40.80	$40.80
Purchase #7	$214.91	10.812%	$238.1461	$238.15	$238.15	$238.10
7 purchase totals =	$744.38		$829.1227	$829.13	$829.05	$829.00