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	$193.40	12.191%	$216.9774	$216.98	$217.00	$217.00
Purchase #2	$151.28	12.131%	$169.6318	$169.63	$169.65	$169.60
Purchase #3	$37.67	11.503%	$42.0032	$42.00	$42.00	$42.00
Purchase #4	$185.55	5.449%	$195.6606	$195.66	$195.65	$195.70
Purchase #5	$92.92	9.584%	$101.8255	$101.83	$101.85	$101.80
Purchase #6	$181.86	3.636%	$188.4724	$188.47	$188.45	$188.50
Purchase #7	$51.30	6.863%	$54.8207	$54.82	$54.80	$54.80
7 purchase totals =	$893.98		$969.3916	$969.39	$969.40	$969.40