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	$247.56	10.587%	$273.7692	$273.77	$273.75	$273.80
Purchase #2	$89.42	11.371%	$99.5879	$99.59	$99.60	$99.60
Purchase #3	$46.93	8.189%	$50.7731	$50.77	$50.75	$50.80
Purchase #4	$106.98	6.304%	$113.724	$113.72	$113.70	$113.70
Purchase #5	$40.73	12.208%	$45.7023	$45.70	$45.70	$45.70
Purchase #6	$137.73	10.822%	$152.6351	$152.64	$152.65	$152.60
Purchase #7	$178.63	5.380%	$188.2403	$188.24	$188.25	$188.20
7 purchase totals =	$847.98		$924.4319	$924.43	$924.40	$924.40