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	$9.90	13.264%	$11.2131	$11.21	$11.20	$11.20
Purchase #2	$30.66	7.555%	$32.9764	$32.98	$33.00	$33.00
Purchase #3	$100.90	10.285%	$111.2776	$111.28	$111.30	$111.30
Purchase #4	$248.59	3.743%	$257.8947	$257.89	$257.90	$257.90
Purchase #5	$74.88	7.639%	$80.6001	$80.60	$80.60	$80.60
Purchase #6	$197.29	13.868%	$224.6502	$224.65	$224.65	$224.70
Purchase #7	$233.66	7.221%	$250.5326	$250.53	$250.55	$250.50
7 purchase totals =	$895.88		$969.1447	$969.14	$969.20	$969.20