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	$33.78	12.391%	$37.9657	$37.97	$37.95	$38.00
Purchase #2	$208.90	8.611%	$226.8884	$226.89	$226.90	$226.90
Purchase #3	$249.46	6.399%	$265.4229	$265.42	$265.40	$265.40
Purchase #4	$186.89	5.121%	$196.4606	$196.46	$196.45	$196.50
Purchase #5	$123.36	13.625%	$140.1678	$140.17	$140.15	$140.20
Purchase #6	$83.90	5.434%	$88.4591	$88.46	$88.45	$88.50
Purchase #7	$95.71	8.818%	$104.1497	$104.15	$104.15	$104.10
7 purchase totals =	$982.00		$1,059.5142	$1,059.52	$1,059.45	$1,059.60