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	$18.98	7.624%	$20.427	$20.43	$20.45	$20.40
Purchase #2	$121.32	3.689%	$125.7955	$125.80	$125.80	$125.80
Purchase #3	$6.38	3.824%	$6.624	$6.62	$6.60	$6.60
Purchase #4	$85.98	11.654%	$96.0001	$96.00	$96.00	$96.00
Purchase #5	$34.76	11.600%	$38.7922	$38.79	$38.80	$38.80
Purchase #6	$102.94	8.474%	$111.6631	$111.66	$111.65	$111.70
Purchase #7	$192.64	4.127%	$200.5903	$200.59	$200.60	$200.60
7 purchase totals =	$563.00		$599.8922	$599.89	$599.90	$599.90