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	$141.72	12.467%	$159.3882	$159.39	$159.40	$159.40
Purchase #2	$123.89	6.225%	$131.6022	$131.60	$131.60	$131.60
Purchase #3	$106.40	9.312%	$116.308	$116.31	$116.30	$116.30
Purchase #4	$19.48	11.157%	$21.6534	$21.65	$21.65	$21.70
Purchase #5	$102.71	12.139%	$115.178	$115.18	$115.20	$115.20
Purchase #6	$129.75	7.696%	$139.7356	$139.74	$139.75	$139.70
Purchase #7	$202.65	6.863%	$216.5579	$216.56	$216.55	$216.60
7 purchase totals =	$826.60		$900.4233	$900.43	$900.45	$900.50