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	$57.68	6.158%	$61.2319	$61.23	$61.25	$61.20
Purchase #2	$82.70	6.861%	$88.374	$88.37	$88.35	$88.40
Purchase #3	$239.96	7.441%	$257.8154	$257.82	$257.80	$257.80
Purchase #4	$42.71	8.620%	$46.3916	$46.39	$46.40	$46.40
Purchase #5	$78.85	9.385%	$86.2501	$86.25	$86.25	$86.30
Purchase #6	$142.58	5.641%	$150.6229	$150.62	$150.60	$150.60
Purchase #7	$25.48	9.390%	$27.8726	$27.87	$27.85	$27.90
7 purchase totals =	$669.96		$718.5585	$718.55	$718.50	$718.60