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	$9.89	4.535%	$10.3385	$10.34	$10.35	$10.30
Purchase #2	$86.83	13.708%	$98.7327	$98.73	$98.75	$98.70
Purchase #3	$151.83	13.521%	$172.3589	$172.36	$172.35	$172.40
Purchase #4	$18.75	12.761%	$21.1427	$21.14	$21.15	$21.10
Purchase #5	$203.39	4.239%	$212.0117	$212.01	$212.00	$212.00
Purchase #6	$92.51	9.516%	$101.3133	$101.31	$101.30	$101.30
Purchase #7	$198.29	3.852%	$205.9281	$205.93	$205.95	$205.90
7 purchase totals =	$761.49		$821.8259	$821.82	$821.85	$821.70