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	$131.90	12.480%	$148.3611	$148.36	$148.35	$148.40
Purchase #2	$40.68	12.209%	$45.6466	$45.65	$45.65	$45.60
Purchase #3	$165.28	6.409%	$175.8728	$175.87	$175.85	$175.90
Purchase #4	$164.91	4.727%	$172.7053	$172.71	$172.70	$172.70
Purchase #5	$19.33	9.208%	$21.1099	$21.11	$21.10	$21.10
Purchase #6	$54.33	9.222%	$59.3403	$59.34	$59.35	$59.30
Purchase #7	$86.89	12.544%	$97.7895	$97.79	$97.80	$97.80
7 purchase totals =	$663.32		$720.8255	$720.83	$720.80	$720.80