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	$10.51	13.168%	$11.894	$11.89	$11.90	$11.90
Purchase #2	$227.76	12.602%	$256.4623	$256.46	$256.45	$256.50
Purchase #3	$109.80	12.686%	$123.7292	$123.73	$123.75	$123.70
Purchase #4	$241.30	4.874%	$253.061	$253.06	$253.05	$253.10
Purchase #5	$165.50	12.638%	$186.4159	$186.42	$186.40	$186.40
Purchase #6	$178.27	5.471%	$188.0232	$188.02	$188.00	$188.00
Purchase #7	$178.48	3.860%	$185.3693	$185.37	$185.35	$185.40
7 purchase totals =	$1,111.62		$1,204.9549	$1,204.95	$1,204.90	$1,205.00