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	$242.91	9.309%	$265.5225	$265.52	$265.50	$265.50
Purchase #2	$138.50	5.731%	$146.4374	$146.44	$146.45	$146.40
Purchase #3	$142.81	8.496%	$154.9431	$154.94	$154.95	$154.90
Purchase #4	$83.71	6.661%	$89.2859	$89.29	$89.30	$89.30
Purchase #5	$220.91	7.394%	$237.2441	$237.24	$237.25	$237.20
Purchase #6	$189.34	10.483%	$209.1885	$209.19	$209.20	$209.20
Purchase #7	$114.64	4.543%	$119.8481	$119.85	$119.85	$119.80
7 purchase totals =	$1,132.82		$1,222.4696	$1,222.47	$1,222.50	$1,222.30