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	$136.34	5.759%	$144.1918	$144.19	$144.20	$144.20
Purchase #2	$126.53	11.350%	$140.8912	$140.89	$140.90	$140.90
Purchase #3	$109.86	12.162%	$123.2212	$123.22	$123.20	$123.20
Purchase #4	$221.29	11.712%	$247.2075	$247.21	$247.20	$247.20
Purchase #5	$80.40	12.553%	$90.4926	$90.49	$90.50	$90.50
Purchase #6	$153.55	3.386%	$158.7492	$158.75	$158.75	$158.70
Purchase #7	$97.56	9.589%	$106.915	$106.92	$106.90	$106.90
7 purchase totals =	$925.53		$1,011.6685	$1,011.67	$1,011.65	$1,011.60