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	$158.86	13.508%	$180.3188	$180.32	$180.30	$180.30
Purchase #2	$240.83	3.638%	$249.5914	$249.59	$249.60	$249.60
Purchase #3	$220.28	12.568%	$247.9648	$247.96	$247.95	$248.00
Purchase #4	$92.72	6.362%	$98.6188	$98.62	$98.60	$98.60
Purchase #5	$126.73	13.788%	$144.2035	$144.20	$144.20	$144.20
Purchase #6	$80.59	12.381%	$90.5678	$90.57	$90.55	$90.60
Purchase #7	$170.44	10.103%	$187.6596	$187.66	$187.65	$187.70
7 purchase totals =	$1,090.45		$1,198.9247	$1,198.92	$1,198.85	$1,199.00