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	$18.96	12.744%	$21.3763	$21.38	$21.40	$21.40
Purchase #2	$36.97	3.511%	$38.268	$38.27	$38.25	$38.30
Purchase #3	$156.62	7.555%	$168.4526	$168.45	$168.45	$168.50
Purchase #4	$53.52	11.370%	$59.6052	$59.61	$59.60	$59.60
Purchase #5	$152.88	6.511%	$162.834	$162.83	$162.85	$162.80
Purchase #6	$175.50	13.591%	$199.3522	$199.35	$199.35	$199.40
Purchase #7	$27.74	6.816%	$29.6308	$29.63	$29.65	$29.60
7 purchase totals =	$622.19		$679.5191	$679.52	$679.55	$679.60