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	$102.51	6.702%	$109.3802	$109.38	$109.40	$109.40
Purchase #2	$16.76	6.696%	$17.8822	$17.88	$17.90	$17.90
Purchase #3	$125.87	9.136%	$137.3695	$137.37	$137.35	$137.40
Purchase #4	$53.65	6.210%	$56.9817	$56.98	$57.00	$57.00
Purchase #5	$246.29	10.543%	$272.2564	$272.26	$272.25	$272.30
Purchase #6	$99.64	12.298%	$111.8937	$111.89	$111.90	$111.90
Purchase #7	$45.49	5.223%	$47.8659	$47.87	$47.85	$47.90
7 purchase totals =	$690.21		$753.6296	$753.63	$753.65	$753.80