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	$48.40	12.461%	$54.4311	$54.43	$54.45	$54.40
Purchase #2	$49.40	3.511%	$51.1344	$51.13	$51.15	$51.10
Purchase #3	$24.69	9.563%	$27.0511	$27.05	$27.05	$27.10
Purchase #4	$243.82	13.142%	$275.8628	$275.86	$275.85	$275.90
Purchase #5	$171.31	5.786%	$181.222	$181.22	$181.20	$181.20
Purchase #6	$135.88	10.727%	$150.4558	$150.46	$150.45	$150.50
Purchase #7	$213.75	12.286%	$240.0113	$240.01	$240.00	$240.00
7 purchase totals =	$887.25		$980.1685	$980.16	$980.15	$980.20