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	$51.41	9.365%	$56.2245	$56.22	$56.20	$56.20
Purchase #2	$143.26	4.717%	$150.0176	$150.02	$150.00	$150.00
Purchase #3	$178.57	5.424%	$188.2556	$188.26	$188.25	$188.30
Purchase #4	$78.83	4.698%	$82.5334	$82.53	$82.55	$82.50
Purchase #5	$186.31	10.547%	$205.9601	$205.96	$205.95	$206.00
Purchase #6	$42.40	8.220%	$45.8853	$45.89	$45.90	$45.90
Purchase #7	$52.35	8.688%	$56.8982	$56.90	$56.90	$56.90
7 purchase totals =	$733.13		$785.7747	$785.78	$785.75	$785.80