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	$18.34	6.542%	$19.5398	$19.54	$19.55	$19.50
Purchase #2	$198.75	10.793%	$220.2011	$220.20	$220.20	$220.20
Purchase #3	$232.78	7.576%	$250.4154	$250.42	$250.40	$250.40
Purchase #4	$54.33	9.499%	$59.4908	$59.49	$59.50	$59.50
Purchase #5	$197.80	8.675%	$214.9592	$214.96	$214.95	$215.00
Purchase #6	$6.82	7.430%	$7.3267	$7.33	$7.35	$7.30
Purchase #7	$54.50	9.266%	$59.55	$59.55	$59.55	$59.60
7 purchase totals =	$763.32		$831.4830	$831.49	$831.50	$831.50