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	$66.28	12.865%	$74.8069	$74.81	$74.80	$74.80
Purchase #2	$142.33	12.658%	$160.3461	$160.35	$160.35	$160.30
Purchase #3	$142.60	13.793%	$162.2688	$162.27	$162.25	$162.30
Purchase #4	$197.85	13.769%	$225.092	$225.09	$225.10	$225.10
Purchase #5	$173.50	5.376%	$182.8274	$182.83	$182.85	$182.80
Purchase #6	$117.81	9.147%	$128.5861	$128.59	$128.60	$128.60
Purchase #7	$162.41	3.168%	$167.5551	$167.56	$167.55	$167.60
7 purchase totals =	$1,002.78		$1,101.4824	$1,101.50	$1,101.50	$1,101.50