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	$164.67	9.566%	$180.4223	$180.42	$180.40	$180.40
Purchase #2	$242.50	5.429%	$255.6653	$255.67	$255.65	$255.70
Purchase #3	$21.82	12.553%	$24.5591	$24.56	$24.55	$24.60
Purchase #4	$90.37	12.329%	$101.5117	$101.51	$101.50	$101.50
Purchase #5	$41.36	3.414%	$42.772	$42.77	$42.75	$42.80
Purchase #6	$27.77	9.135%	$30.3068	$30.31	$30.30	$30.30
Purchase #7	$142.91	7.232%	$153.2453	$153.25	$153.25	$153.20
7 purchase totals =	$731.40		$788.4825	$788.49	$788.40	$788.50