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	$82.60	9.140%	$90.1496	$90.15	$90.15	$90.10
Purchase #2	$98.93	6.759%	$105.6167	$105.62	$105.60	$105.60
Purchase #3	$121.28	4.819%	$127.1245	$127.12	$127.10	$127.10
Purchase #4	$114.60	4.210%	$119.4247	$119.42	$119.40	$119.40
Purchase #5	$104.63	9.197%	$114.2528	$114.25	$114.25	$114.30
Purchase #6	$207.98	9.795%	$228.3516	$228.35	$228.35	$228.40
Purchase #7	$178.99	12.275%	$200.961	$200.96	$200.95	$201.00
7 purchase totals =	$909.01		$985.8809	$985.87	$985.80	$985.90