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	$6.75	12.712%	$7.6081	$7.61	$7.60	$7.60
Purchase #2	$133.81	3.403%	$138.3636	$138.36	$138.35	$138.40
Purchase #3	$77.85	5.758%	$82.3326	$82.33	$82.35	$82.30
Purchase #4	$150.72	11.502%	$168.0558	$168.06	$168.05	$168.10
Purchase #5	$164.31	8.641%	$178.508	$178.51	$178.50	$178.50
Purchase #6	$74.92	5.425%	$78.9844	$78.98	$79.00	$79.00
Purchase #7	$171.88	4.452%	$179.5321	$179.53	$179.55	$179.50
7 purchase totals =	$780.24		$833.3846	$833.38	$833.40	$833.40