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	$166.92	12.798%	$188.2824	$188.28	$188.30	$188.30
Purchase #2	$136.86	11.176%	$152.1555	$152.16	$152.15	$152.20
Purchase #3	$54.94	7.301%	$58.9512	$58.95	$58.95	$59.00
Purchase #4	$236.50	7.339%	$253.8567	$253.86	$253.85	$253.90
Purchase #5	$90.57	6.549%	$96.5014	$96.50	$96.50	$96.50
Purchase #6	$24.77	11.344%	$27.5799	$27.58	$27.60	$27.60
Purchase #7	$75.96	3.696%	$78.7675	$78.77	$78.75	$78.80
7 purchase totals =	$786.52		$856.0946	$856.10	$856.10	$856.30