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	$237.57	6.364%	$252.689	$252.69	$252.70	$252.70
Purchase #2	$245.94	9.646%	$269.6634	$269.66	$269.65	$269.70
Purchase #3	$242.25	5.381%	$255.2855	$255.29	$255.30	$255.30
Purchase #4	$49.97	12.754%	$56.3432	$56.34	$56.35	$56.30
Purchase #5	$38.82	11.745%	$43.3794	$43.38	$43.40	$43.40
Purchase #6	$131.71	8.385%	$142.7539	$142.75	$142.75	$142.80
Purchase #7	$74.63	7.271%	$80.0563	$80.06	$80.05	$80.10
7 purchase totals =	$1,020.89		$1,100.1707	$1,100.17	$1,100.20	$1,100.30