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	$100.87	8.613%	$109.5579	$109.56	$109.55	$109.60
Purchase #2	$211.67	10.805%	$234.5409	$234.54	$234.55	$234.50
Purchase #3	$102.34	6.729%	$109.2265	$109.23	$109.25	$109.20
Purchase #4	$207.44	11.387%	$231.0612	$231.06	$231.05	$231.10
Purchase #5	$62.82	7.249%	$67.3738	$67.37	$67.35	$67.40
Purchase #6	$78.85	3.521%	$81.6263	$81.63	$81.65	$81.60
Purchase #7	$20.58	11.124%	$22.8693	$22.87	$22.85	$22.90
7 purchase totals =	$784.57		$856.2559	$856.26	$856.25	$856.30