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	$21.32	3.232%	$22.0091	$22.01	$22.00	$22.00
Purchase #2	$38.47	3.728%	$39.9042	$39.90	$39.90	$39.90
Purchase #3	$190.78	7.781%	$205.6246	$205.62	$205.60	$205.60
Purchase #4	$151.25	7.452%	$162.5212	$162.52	$162.50	$162.50
Purchase #5	$108.69	13.309%	$123.1556	$123.16	$123.15	$123.20
Purchase #6	$228.38	6.402%	$243.0009	$243.00	$243.00	$243.00
Purchase #7	$33.36	6.598%	$35.5611	$35.56	$35.55	$35.60
7 purchase totals =	$772.25		$831.7767	$831.77	$831.70	$831.80