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	$113.54	8.792%	$123.5224	$123.52	$123.50	$123.50
Purchase #2	$149.99	5.204%	$157.7955	$157.80	$157.80	$157.80
Purchase #3	$215.25	7.479%	$231.3485	$231.35	$231.35	$231.30
Purchase #4	$31.59	3.275%	$32.6246	$32.62	$32.60	$32.60
Purchase #5	$37.71	5.486%	$39.7788	$39.78	$39.80	$39.80
Purchase #6	$147.25	12.837%	$166.1525	$166.15	$166.15	$166.20
Purchase #7	$99.39	5.583%	$104.9389	$104.94	$104.95	$104.90
7 purchase totals =	$794.72		$856.1612	$856.16	$856.15	$856.10