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	$40.31	10.456%	$44.5248	$44.52	$44.50	$44.50
Purchase #2	$242.89	11.169%	$270.0184	$270.02	$270.00	$270.00
Purchase #3	$157.85	8.618%	$171.4535	$171.45	$171.45	$171.50
Purchase #4	$32.82	3.156%	$33.8558	$33.86	$33.85	$33.90
Purchase #5	$213.39	8.794%	$232.1555	$232.16	$232.15	$232.20
Purchase #6	$37.93	5.773%	$40.1197	$40.12	$40.10	$40.10
Purchase #7	$41.72	3.151%	$43.0346	$43.03	$43.05	$43.00
7 purchase totals =	$766.91		$835.1623	$835.16	$835.10	$835.20