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	$247.47	11.456%	$275.8202	$275.82	$275.80	$275.80
Purchase #2	$54.30	10.250%	$59.8658	$59.87	$59.85	$59.90
Purchase #3	$162.84	12.137%	$182.6039	$182.60	$182.60	$182.60
Purchase #4	$52.82	12.849%	$59.6068	$59.61	$59.60	$59.60
Purchase #5	$36.33	8.552%	$39.4369	$39.44	$39.45	$39.40
Purchase #6	$67.71	6.333%	$71.9981	$72.00	$72.00	$72.00
Purchase #7	$84.30	4.337%	$87.9561	$87.96	$87.95	$88.00
7 purchase totals =	$705.77		$777.2878	$777.30	$777.25	$777.30