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	$126.89	10.244%	$139.8886	$139.89	$139.90	$139.90
Purchase #2	$115.72	8.434%	$125.4798	$125.48	$125.50	$125.50
Purchase #3	$197.43	12.673%	$222.4503	$222.45	$222.45	$222.50
Purchase #4	$237.38	8.670%	$257.9608	$257.96	$257.95	$258.00
Purchase #5	$107.80	7.152%	$115.5099	$115.51	$115.50	$115.50
Purchase #6	$66.44	8.530%	$72.1073	$72.11	$72.10	$72.10
Purchase #7	$33.39	7.825%	$36.0028	$36.00	$36.00	$36.00
7 purchase totals =	$885.05		$969.3995	$969.40	$969.40	$969.50