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	$159.63	12.770%	$180.0148	$180.01	$180.00	$180.00
Purchase #2	$100.45	8.755%	$109.2444	$109.24	$109.25	$109.20
Purchase #3	$81.62	9.156%	$89.0931	$89.09	$89.10	$89.10
Purchase #4	$104.66	4.462%	$109.3299	$109.33	$109.35	$109.30
Purchase #5	$238.61	3.125%	$246.0666	$246.07	$246.05	$246.10
Purchase #6	$12.77	6.360%	$13.5822	$13.58	$13.60	$13.60
Purchase #7	$52.56	9.460%	$57.5322	$57.53	$57.55	$57.50
7 purchase totals =	$750.30		$804.8632	$804.85	$804.90	$804.80