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	$90.45	5.440%	$95.3705	$95.37	$95.35	$95.40
Purchase #2	$114.28	4.281%	$119.1723	$119.17	$119.15	$119.20
Purchase #3	$94.25	7.306%	$101.1359	$101.14	$101.15	$101.10
Purchase #4	$171.43	10.712%	$189.7936	$189.79	$189.80	$189.80
Purchase #5	$158.85	8.651%	$172.5921	$172.59	$172.60	$172.60
Purchase #6	$216.43	12.503%	$243.4902	$243.49	$243.50	$243.50
Purchase #7	$158.30	7.415%	$170.0379	$170.04	$170.05	$170.00
7 purchase totals =	$1,003.99		$1,091.5925	$1,091.59	$1,091.60	$1,091.60