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	$69.33	12.669%	$78.1134	$78.11	$78.10	$78.10
Purchase #2	$241.67	11.705%	$269.9575	$269.96	$269.95	$270.00
Purchase #3	$122.81	8.240%	$132.9295	$132.93	$132.95	$132.90
Purchase #4	$160.90	3.545%	$166.6039	$166.60	$166.60	$166.60
Purchase #5	$81.68	4.364%	$85.2445	$85.24	$85.25	$85.20
Purchase #6	$249.80	9.510%	$273.556	$273.56	$273.55	$273.60
Purchase #7	$164.85	10.464%	$182.0999	$182.10	$182.10	$182.10
7 purchase totals =	$1,091.04		$1,188.5047	$1,188.50	$1,188.50	$1,188.50