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	$93.86	6.150%	$99.6324	$99.63	$99.65	$99.60
Purchase #2	$138.54	9.536%	$151.7512	$151.75	$151.75	$151.80
Purchase #3	$158.90	3.557%	$164.5521	$164.55	$164.55	$164.60
Purchase #4	$74.50	10.567%	$82.3724	$82.37	$82.35	$82.40
Purchase #5	$25.62	12.735%	$28.8827	$28.88	$28.90	$28.90
Purchase #6	$116.43	8.332%	$126.1309	$126.13	$126.15	$126.10
Purchase #7	$163.64	9.281%	$178.8274	$178.83	$178.85	$178.80
7 purchase totals =	$771.49		$832.1491	$832.14	$832.20	$832.20