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	$167.81	7.560%	$180.4964	$180.50	$180.50	$180.50
Purchase #2	$66.59	8.421%	$72.1975	$72.20	$72.20	$72.20
Purchase #3	$145.38	7.219%	$155.875	$155.88	$155.90	$155.90
Purchase #4	$38.76	12.152%	$43.4701	$43.47	$43.45	$43.50
Purchase #5	$70.32	4.510%	$73.4914	$73.49	$73.50	$73.50
Purchase #6	$163.93	10.164%	$180.5918	$180.59	$180.60	$180.60
Purchase #7	$117.94	11.731%	$131.7755	$131.78	$131.80	$131.80
7 purchase totals =	$770.73		$837.8977	$837.91	$837.95	$838.00