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	$110.86	5.370%	$116.8132	$116.81	$116.80	$116.80
Purchase #2	$162.34	7.741%	$174.9067	$174.91	$174.90	$174.90
Purchase #3	$163.48	3.778%	$169.6563	$169.66	$169.65	$169.70
Purchase #4	$51.95	10.533%	$57.4219	$57.42	$57.40	$57.40
Purchase #5	$138.85	8.847%	$151.1341	$151.13	$151.15	$151.10
Purchase #6	$137.62	6.436%	$146.4772	$146.48	$146.50	$146.50
Purchase #7	$68.71	5.488%	$72.4808	$72.48	$72.50	$72.50
7 purchase totals =	$833.81		$888.8902	$888.89	$888.90	$888.90