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	$155.33	10.246%	$171.2451	$171.25	$171.25	$171.20
Purchase #2	$210.50	11.583%	$234.8822	$234.88	$234.90	$234.90
Purchase #3	$91.72	13.171%	$103.8004	$103.80	$103.80	$103.80
Purchase #4	$26.74	8.203%	$28.9335	$28.93	$28.95	$28.90
Purchase #5	$148.82	12.405%	$167.2811	$167.28	$167.30	$167.30
Purchase #6	$151.86	5.694%	$160.5069	$160.51	$160.50	$160.50
Purchase #7	$65.72	6.401%	$69.9267	$69.93	$69.95	$69.90
7 purchase totals =	$850.69		$936.5759	$936.58	$936.65	$936.50