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	$136.75	5.850%	$144.7499	$144.75	$144.75	$144.70
Purchase #2	$164.25	4.264%	$171.2536	$171.25	$171.25	$171.30
Purchase #3	$238.91	13.864%	$272.0325	$272.03	$272.05	$272.00
Purchase #4	$185.73	7.262%	$199.2177	$199.22	$199.20	$199.20
Purchase #5	$171.42	4.377%	$178.9231	$178.92	$178.90	$178.90
Purchase #6	$173.47	10.437%	$191.5751	$191.58	$191.60	$191.60
Purchase #7	$143.27	5.132%	$150.6226	$150.62	$150.60	$150.60
7 purchase totals =	$1,213.80		$1,308.3745	$1,308.37	$1,308.35	$1,308.30