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	$109.85	9.456%	$120.2374	$120.24	$120.25	$120.20
Purchase #2	$96.45	4.241%	$100.5404	$100.54	$100.55	$100.50
Purchase #3	$122.74	9.518%	$134.4224	$134.42	$134.40	$134.40
Purchase #4	$74.71	9.611%	$81.8904	$81.89	$81.90	$81.90
Purchase #5	$175.62	5.851%	$185.8955	$185.90	$185.90	$185.90
Purchase #6	$50.37	5.750%	$53.2663	$53.27	$53.25	$53.30
Purchase #7	$79.42	3.356%	$82.0853	$82.09	$82.10	$82.10
7 purchase totals =	$709.16		$758.3377	$758.35	$758.35	$758.30