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	$61.75	9.392%	$67.5496	$67.55	$67.55	$67.50
Purchase #2	$181.78	10.364%	$200.6197	$200.62	$200.60	$200.60
Purchase #3	$43.94	4.766%	$46.0342	$46.03	$46.05	$46.00
Purchase #4	$13.38	13.474%	$15.1828	$15.18	$15.20	$15.20
Purchase #5	$193.62	8.589%	$210.25	$210.25	$210.25	$210.30
Purchase #6	$153.48	9.715%	$168.3906	$168.39	$168.40	$168.40
Purchase #7	$79.53	11.719%	$88.8501	$88.85	$88.85	$88.90
7 purchase totals =	$727.48		$796.8770	$796.87	$796.90	$796.90