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	$64.94	12.109%	$72.8036	$72.80	$72.80	$72.80
Purchase #2	$121.96	12.335%	$137.0038	$137.00	$137.00	$137.00
Purchase #3	$86.80	4.759%	$90.9308	$90.93	$90.95	$90.90
Purchase #4	$169.32	10.652%	$187.356	$187.36	$187.35	$187.40
Purchase #5	$42.29	10.331%	$46.659	$46.66	$46.65	$46.70
Purchase #6	$220.86	10.220%	$243.4319	$243.43	$243.45	$243.40
Purchase #7	$55.40	13.136%	$62.6773	$62.68	$62.70	$62.70
7 purchase totals =	$761.57		$840.8624	$840.86	$840.90	$840.90