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	$184.78	13.311%	$209.3761	$209.38	$209.40	$209.40
Purchase #2	$82.63	7.141%	$88.5306	$88.53	$88.55	$88.50
Purchase #3	$196.38	12.531%	$220.9884	$220.99	$221.00	$221.00
Purchase #4	$48.77	10.681%	$53.9791	$53.98	$54.00	$54.00
Purchase #5	$183.89	10.638%	$203.4522	$203.45	$203.45	$203.50
Purchase #6	$71.39	9.527%	$78.1913	$78.19	$78.20	$78.20
Purchase #7	$19.97	4.601%	$20.8888	$20.89	$20.90	$20.90
7 purchase totals =	$787.81		$875.4065	$875.41	$875.50	$875.50