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	$12.27	9.656%	$13.4548	$13.45	$13.45	$13.50
Purchase #2	$35.89	5.463%	$37.8507	$37.85	$37.85	$37.90
Purchase #3	$249.76	13.405%	$283.2403	$283.24	$283.25	$283.20
Purchase #4	$134.78	6.222%	$143.166	$143.17	$143.15	$143.20
Purchase #5	$124.33	5.834%	$131.5834	$131.58	$131.60	$131.60
Purchase #6	$158.67	5.441%	$167.3032	$167.30	$167.30	$167.30
Purchase #7	$47.54	7.832%	$51.2633	$51.26	$51.25	$51.30
7 purchase totals =	$763.24		$827.8617	$827.85	$827.85	$828.00