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	$147.88	8.253%	$160.0845	$160.08	$160.10	$160.10
Purchase #2	$53.59	10.817%	$59.3868	$59.39	$59.40	$59.40
Purchase #3	$20.94	3.327%	$21.6367	$21.64	$21.65	$21.60
Purchase #4	$69.30	13.199%	$78.4469	$78.45	$78.45	$78.40
Purchase #5	$90.89	13.402%	$103.0711	$103.07	$103.05	$103.10
Purchase #6	$143.84	9.589%	$157.6328	$157.63	$157.65	$157.60
Purchase #7	$36.82	12.831%	$41.5444	$41.54	$41.55	$41.50
7 purchase totals =	$563.26		$621.8032	$621.80	$621.85	$621.70