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	$161.81	10.554%	$178.8874	$178.89	$178.90	$178.90
Purchase #2	$189.55	6.503%	$201.8764	$201.88	$201.90	$201.90
Purchase #3	$196.73	3.848%	$204.3002	$204.30	$204.30	$204.30
Purchase #4	$166.65	10.573%	$184.2699	$184.27	$184.25	$184.30
Purchase #5	$11.86	5.405%	$12.501	$12.50	$12.50	$12.50
Purchase #6	$59.72	10.530%	$66.0085	$66.01	$66.00	$66.00
Purchase #7	$38.29	10.586%	$42.3434	$42.34	$42.35	$42.30
7 purchase totals =	$824.61		$890.1868	$890.19	$890.20	$890.20