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	$102.89	8.407%	$111.54	$111.54	$111.55	$111.50
Purchase #2	$180.49	11.284%	$200.8565	$200.86	$200.85	$200.90
Purchase #3	$162.90	5.487%	$171.8383	$171.84	$171.85	$171.80
Purchase #4	$13.67	10.669%	$15.1285	$15.13	$15.15	$15.10
Purchase #5	$226.28	12.180%	$253.8409	$253.84	$253.85	$253.80
Purchase #6	$130.49	8.811%	$141.9875	$141.99	$142.00	$142.00
Purchase #7	$87.84	7.500%	$94.428	$94.43	$94.45	$94.40
7 purchase totals =	$904.56		$989.6197	$989.63	$989.70	$989.50