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	$131.71	3.517%	$136.3422	$136.34	$136.35	$136.30
Purchase #2	$233.39	11.324%	$259.8191	$259.82	$259.80	$259.80
Purchase #3	$173.65	6.319%	$184.6229	$184.62	$184.60	$184.60
Purchase #4	$16.52	5.688%	$17.4597	$17.46	$17.45	$17.50
Purchase #5	$28.32	13.441%	$32.1265	$32.13	$32.15	$32.10
Purchase #6	$32.26	4.516%	$33.7169	$33.72	$33.70	$33.70
Purchase #7	$147.35	13.649%	$167.4618	$167.46	$167.45	$167.50
7 purchase totals =	$763.20		$831.5491	$831.55	$831.50	$831.50