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	$99.41	6.393%	$105.7653	$105.77	$105.75	$105.80
Purchase #2	$95.59	3.804%	$99.2262	$99.23	$99.25	$99.20
Purchase #3	$115.64	9.584%	$126.7229	$126.72	$126.70	$126.70
Purchase #4	$73.56	6.813%	$78.5716	$78.57	$78.55	$78.60
Purchase #5	$23.93	3.591%	$24.7893	$24.79	$24.80	$24.80
Purchase #6	$131.29	11.599%	$146.5183	$146.52	$146.50	$146.50
Purchase #7	$121.69	5.485%	$128.3647	$128.36	$128.35	$128.40
7 purchase totals =	$661.11		$709.9583	$709.96	$709.90	$710.00