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	$100.86	4.670%	$105.5702	$105.57	$105.55	$105.60
Purchase #2	$99.84	13.433%	$113.2515	$113.25	$113.25	$113.30
Purchase #3	$127.62	9.576%	$139.8409	$139.84	$139.85	$139.80
Purchase #4	$35.88	12.255%	$40.2771	$40.28	$40.30	$40.30
Purchase #5	$111.46	7.297%	$119.5932	$119.59	$119.60	$119.60
Purchase #6	$145.94	10.227%	$160.8653	$160.87	$160.85	$160.90
Purchase #7	$96.88	4.813%	$101.5428	$101.54	$101.55	$101.50
7 purchase totals =	$718.48		$780.9410	$780.94	$780.95	$781.00