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	$173.73	6.639%	$185.2639	$185.26	$185.25	$185.30
Purchase #2	$138.67	4.186%	$144.4747	$144.47	$144.45	$144.50
Purchase #3	$123.99	6.612%	$132.1882	$132.19	$132.20	$132.20
Purchase #4	$185.96	12.505%	$209.2143	$209.21	$209.20	$209.20
Purchase #5	$137.67	5.200%	$144.8288	$144.83	$144.85	$144.80
Purchase #6	$213.63	11.446%	$238.0821	$238.08	$238.10	$238.10
Purchase #7	$51.65	10.694%	$57.1735	$57.17	$57.15	$57.20
7 purchase totals =	$1,025.30		$1,111.2255	$1,111.21	$1,111.20	$1,111.30