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	$151.93	9.654%	$166.5973	$166.60	$166.60	$166.60
Purchase #2	$129.82	11.702%	$145.0115	$145.01	$145.00	$145.00
Purchase #3	$174.25	3.123%	$179.6918	$179.69	$179.70	$179.70
Purchase #4	$154.38	8.401%	$167.3495	$167.35	$167.35	$167.30
Purchase #5	$93.36	9.567%	$102.2918	$102.29	$102.30	$102.30
Purchase #6	$112.60	12.434%	$126.6007	$126.60	$126.60	$126.60
Purchase #7	$233.72	4.247%	$243.6461	$243.65	$243.65	$243.60
7 purchase totals =	$1,050.06		$1,131.1887	$1,131.19	$1,131.20	$1,131.10