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	$110.66	9.441%	$121.1074	$121.11	$121.10	$121.10
Purchase #2	$86.38	8.873%	$94.0445	$94.04	$94.05	$94.00
Purchase #3	$178.41	12.262%	$200.2866	$200.29	$200.30	$200.30
Purchase #4	$57.78	3.307%	$59.6908	$59.69	$59.70	$59.70
Purchase #5	$44.79	10.686%	$49.5763	$49.58	$49.60	$49.60
Purchase #6	$174.64	12.706%	$196.8298	$196.83	$196.85	$196.80
Purchase #7	$196.31	9.269%	$214.506	$214.51	$214.50	$214.50
7 purchase totals =	$848.97		$936.0414	$936.05	$936.10	$936.00