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	$246.32	13.187%	$278.8022	$278.80	$278.80	$278.80
Purchase #2	$241.89	10.761%	$267.9198	$267.92	$267.90	$267.90
Purchase #3	$5.31	8.843%	$5.7796	$5.78	$5.80	$5.80
Purchase #4	$87.96	8.745%	$95.6521	$95.65	$95.65	$95.70
Purchase #5	$133.65	6.384%	$142.1822	$142.18	$142.20	$142.20
Purchase #6	$64.33	11.699%	$71.856	$71.86	$71.85	$71.90
Purchase #7	$87.35	3.423%	$90.34	$90.34	$90.35	$90.30
7 purchase totals =	$866.81		$952.5319	$952.53	$952.55	$952.60