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	$245.48	4.271%	$255.9645	$255.96	$255.95	$256.00
Purchase #2	$54.43	8.539%	$59.0778	$59.08	$59.10	$59.10
Purchase #3	$112.59	6.646%	$120.0727	$120.07	$120.05	$120.10
Purchase #4	$19.93	6.167%	$21.1591	$21.16	$21.15	$21.20
Purchase #5	$46.71	11.192%	$51.9378	$51.94	$51.95	$51.90
Purchase #6	$232.79	7.513%	$250.2795	$250.28	$250.30	$250.30
Purchase #7	$219.38	12.864%	$247.601	$247.60	$247.60	$247.60
7 purchase totals =	$931.31		$1,006.0924	$1,006.09	$1,006.10	$1,006.20