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	$123.71	8.723%	$134.5012	$134.50	$134.50	$134.50
Purchase #2	$146.86	11.689%	$164.0265	$164.03	$164.05	$164.00
Purchase #3	$94.55	12.235%	$106.1182	$106.12	$106.10	$106.10
Purchase #4	$103.72	5.163%	$109.0751	$109.08	$109.10	$109.10
Purchase #5	$38.53	6.504%	$41.036	$41.04	$41.05	$41.00
Purchase #6	$124.32	12.591%	$139.9731	$139.97	$139.95	$140.00
Purchase #7	$145.29	5.704%	$153.5773	$153.58	$153.60	$153.60
7 purchase totals =	$776.98		$848.3074	$848.32	$848.35	$848.30