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	$245.67	13.765%	$279.4865	$279.49	$279.50	$279.50
Purchase #2	$145.59	12.543%	$163.8514	$163.85	$163.85	$163.90
Purchase #3	$83.38	8.405%	$90.3881	$90.39	$90.40	$90.40
Purchase #4	$38.65	9.122%	$42.1757	$42.18	$42.20	$42.20
Purchase #5	$207.41	12.620%	$233.5851	$233.59	$233.60	$233.60
Purchase #6	$232.36	3.617%	$240.7645	$240.76	$240.75	$240.80
Purchase #7	$159.47	7.639%	$171.6519	$171.65	$171.65	$171.70
7 purchase totals =	$1,112.53		$1,221.9032	$1,221.91	$1,221.95	$1,222.10