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	$136.60	11.170%	$151.8582	$151.86	$151.85	$151.90
Purchase #2	$155.86	10.472%	$172.1817	$172.18	$172.20	$172.20
Purchase #3	$168.59	7.167%	$180.6728	$180.67	$180.65	$180.70
Purchase #4	$27.33	5.155%	$28.7389	$28.74	$28.75	$28.70
Purchase #5	$125.49	12.204%	$140.8048	$140.80	$140.80	$140.80
Purchase #6	$35.52	7.798%	$38.2898	$38.29	$38.30	$38.30
Purchase #7	$103.62	5.583%	$109.4051	$109.41	$109.40	$109.40
7 purchase totals =	$753.01		$821.9513	$821.95	$821.95	$822.00