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	$47.84	5.305%	$50.3779	$50.38	$50.40	$50.40
Purchase #2	$227.52	7.152%	$243.7922	$243.79	$243.80	$243.80
Purchase #3	$154.25	9.158%	$168.3762	$168.38	$168.40	$168.40
Purchase #4	$75.66	10.850%	$83.8691	$83.87	$83.85	$83.90
Purchase #5	$145.93	6.325%	$155.1601	$155.16	$155.15	$155.20
Purchase #6	$224.82	5.360%	$236.8704	$236.87	$236.85	$236.90
Purchase #7	$66.59	9.295%	$72.7795	$72.78	$72.80	$72.80
7 purchase totals =	$942.61		$1,011.2254	$1,011.23	$1,011.25	$1,011.40