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	$25.40	11.301%	$28.2705	$28.27	$28.25	$28.30
Purchase #2	$109.33	12.459%	$122.9514	$122.95	$122.95	$123.00
Purchase #3	$107.53	5.312%	$113.242	$113.24	$113.25	$113.20
Purchase #4	$56.98	4.540%	$59.5669	$59.57	$59.55	$59.60
Purchase #5	$73.66	6.689%	$78.5871	$78.59	$78.60	$78.60
Purchase #6	$28.27	5.376%	$29.7898	$29.79	$29.80	$29.80
Purchase #7	$88.92	13.553%	$100.9713	$100.97	$100.95	$101.00
7 purchase totals =	$490.09		$533.3790	$533.38	$533.35	$533.50