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	$250.82	11.665%	$280.0782	$280.08	$280.10	$280.10
Purchase #2	$90.62	10.604%	$100.2293	$100.23	$100.25	$100.20
Purchase #3	$153.67	13.249%	$174.0297	$174.03	$174.05	$174.00
Purchase #4	$31.29	8.210%	$33.8589	$33.86	$33.85	$33.90
Purchase #5	$72.31	13.621%	$82.1593	$82.16	$82.15	$82.20
Purchase #6	$40.47	5.722%	$42.7857	$42.79	$42.80	$42.80
Purchase #7	$116.72	6.260%	$124.0267	$124.03	$124.05	$124.00
7 purchase totals =	$755.90		$837.1678	$837.18	$837.25	$837.20