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	$102.76	6.786%	$109.7333	$109.73	$109.75	$109.70
Purchase #2	$122.26	9.307%	$133.6387	$133.64	$133.65	$133.60
Purchase #3	$231.98	12.572%	$261.1445	$261.14	$261.15	$261.10
Purchase #4	$81.96	4.377%	$85.5474	$85.55	$85.55	$85.50
Purchase #5	$128.89	3.754%	$133.7285	$133.73	$133.75	$133.70
Purchase #6	$76.94	10.684%	$85.1603	$85.16	$85.15	$85.20
Purchase #7	$42.27	3.827%	$43.8877	$43.89	$43.90	$43.90
7 purchase totals =	$787.06		$852.8404	$852.84	$852.90	$852.70