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	$9.40	3.513%	$9.7302	$9.73	$9.75	$9.70
Purchase #2	$169.57	5.840%	$179.4729	$179.47	$179.45	$179.50
Purchase #3	$123.66	8.552%	$134.2354	$134.24	$134.25	$134.20
Purchase #4	$109.54	12.297%	$123.0101	$123.01	$123.00	$123.00
Purchase #5	$100.74	7.614%	$108.4103	$108.41	$108.40	$108.40
Purchase #6	$44.31	8.844%	$48.2288	$48.23	$48.25	$48.20
Purchase #7	$71.47	10.358%	$78.8729	$78.87	$78.85	$78.90
7 purchase totals =	$628.69		$681.9606	$681.96	$681.95	$681.90