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	$26.27	8.831%	$28.5899	$28.59	$28.60	$28.60
Purchase #2	$122.64	13.534%	$139.2381	$139.24	$139.25	$139.20
Purchase #3	$193.93	6.287%	$206.1224	$206.12	$206.10	$206.10
Purchase #4	$36.40	13.546%	$41.3307	$41.33	$41.35	$41.30
Purchase #5	$114.45	7.772%	$123.3451	$123.35	$123.35	$123.30
Purchase #6	$53.26	11.781%	$59.5346	$59.53	$59.55	$59.50
Purchase #7	$16.76	6.795%	$17.8988	$17.90	$17.90	$17.90
7 purchase totals =	$563.71		$616.0596	$616.06	$616.10	$615.90