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	$10.52	9.475%	$11.5168	$11.52	$11.50	$11.50
Purchase #2	$221.92	6.585%	$236.5334	$236.53	$236.55	$236.50
Purchase #3	$234.90	12.397%	$264.0206	$264.02	$264.00	$264.00
Purchase #4	$247.49	7.417%	$265.8463	$265.85	$265.85	$265.80
Purchase #5	$14.78	4.806%	$15.4903	$15.49	$15.50	$15.50
Purchase #6	$47.83	13.140%	$54.1149	$54.11	$54.10	$54.10
Purchase #7	$127.42	13.688%	$144.8612	$144.86	$144.85	$144.90
7 purchase totals =	$904.86		$992.3835	$992.38	$992.35	$992.30