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	$22.92	5.751%	$24.2381	$24.24	$24.25	$24.20
Purchase #2	$155.72	8.368%	$168.7506	$168.75	$168.75	$168.80
Purchase #3	$148.82	9.126%	$162.4013	$162.40	$162.40	$162.40
Purchase #4	$147.66	3.546%	$152.896	$152.90	$152.90	$152.90
Purchase #5	$130.61	5.398%	$137.6603	$137.66	$137.65	$137.70
Purchase #6	$77.25	4.720%	$80.8962	$80.90	$80.90	$80.90
Purchase #7	$10.66	11.495%	$11.8854	$11.89	$11.90	$11.90
7 purchase totals =	$693.64		$738.7279	$738.74	$738.75	$738.80