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	$89.68	12.489%	$100.8801	$100.88	$100.90	$100.90
Purchase #2	$216.60	11.671%	$241.8794	$241.88	$241.90	$241.90
Purchase #3	$31.52	4.124%	$32.8199	$32.82	$32.80	$32.80
Purchase #4	$154.36	3.610%	$159.9324	$159.93	$159.95	$159.90
Purchase #5	$154.39	5.397%	$162.7224	$162.72	$162.70	$162.70
Purchase #6	$218.25	4.653%	$228.4052	$228.41	$228.40	$228.40
Purchase #7	$82.52	5.403%	$86.9786	$86.98	$87.00	$87.00
7 purchase totals =	$947.32		$1,013.6180	$1,013.62	$1,013.65	$1,013.60