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	$33.87	13.656%	$38.4953	$38.50	$38.50	$38.50
Purchase #2	$82.51	9.754%	$90.558	$90.56	$90.55	$90.60
Purchase #3	$24.46	7.325%	$26.2517	$26.25	$26.25	$26.30
Purchase #4	$104.65	9.296%	$114.3783	$114.38	$114.40	$114.40
Purchase #5	$194.89	12.555%	$219.3584	$219.36	$219.35	$219.40
Purchase #6	$109.86	12.528%	$123.6233	$123.62	$123.60	$123.60
Purchase #7	$206.51	12.324%	$231.9603	$231.96	$231.95	$232.00
7 purchase totals =	$756.75		$844.6253	$844.63	$844.60	$844.80