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	$63.53	4.374%	$66.3088	$66.31	$66.30	$66.30
Purchase #2	$233.83	11.677%	$261.1343	$261.13	$261.15	$261.10
Purchase #3	$221.25	8.489%	$240.0319	$240.03	$240.05	$240.00
Purchase #4	$119.69	11.615%	$133.592	$133.59	$133.60	$133.60
Purchase #5	$113.59	6.617%	$121.1063	$121.11	$121.10	$121.10
Purchase #6	$140.63	7.277%	$150.8636	$150.86	$150.85	$150.90
Purchase #7	$87.50	13.548%	$99.3545	$99.35	$99.35	$99.40
7 purchase totals =	$980.02		$1,072.3914	$1,072.38	$1,072.40	$1,072.40