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	$131.51	4.309%	$137.1768	$137.18	$137.20	$137.20
Purchase #2	$208.97	5.239%	$219.9179	$219.92	$219.90	$219.90
Purchase #3	$105.90	3.737%	$109.8575	$109.86	$109.85	$109.90
Purchase #4	$102.25	11.174%	$113.6754	$113.68	$113.70	$113.70
Purchase #5	$25.53	7.115%	$27.3465	$27.35	$27.35	$27.30
Purchase #6	$38.64	7.394%	$41.497	$41.50	$41.50	$41.50
Purchase #7	$82.82	8.107%	$89.5342	$89.53	$89.55	$89.50
7 purchase totals =	$695.62		$739.0053	$739.02	$739.05	$739.00