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	$161.93	5.500%	$170.8362	$170.84	$170.85	$170.80
Purchase #2	$86.57	5.377%	$91.2249	$91.22	$91.20	$91.20
Purchase #3	$132.32	6.111%	$140.4061	$140.41	$140.40	$140.40
Purchase #4	$70.83	11.211%	$78.7708	$78.77	$78.75	$78.80
Purchase #5	$121.45	9.122%	$132.5287	$132.53	$132.55	$132.50
Purchase #6	$86.34	3.676%	$89.5139	$89.51	$89.50	$89.50
Purchase #7	$204.86	9.349%	$224.0124	$224.01	$224.00	$224.00
7 purchase totals =	$864.30		$927.2930	$927.29	$927.25	$927.20