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	$92.32	11.733%	$103.1519	$103.15	$103.15	$103.20
Purchase #2	$135.46	12.843%	$152.8571	$152.86	$152.85	$152.90
Purchase #3	$38.27	12.660%	$43.115	$43.12	$43.10	$43.10
Purchase #4	$41.61	9.491%	$45.5592	$45.56	$45.55	$45.60
Purchase #5	$174.41	3.703%	$180.8684	$180.87	$180.85	$180.90
Purchase #6	$248.59	7.589%	$267.4555	$267.46	$267.45	$267.50
Purchase #7	$68.30	8.402%	$74.0386	$74.04	$74.05	$74.00
7 purchase totals =	$798.96		$867.0457	$867.06	$867.00	$867.20