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	$50.95	12.617%	$57.3784	$57.38	$57.40	$57.40
Purchase #2	$177.39	10.616%	$196.2217	$196.22	$196.20	$196.20
Purchase #3	$180.49	5.712%	$190.7996	$190.80	$190.80	$190.80
Purchase #4	$60.98	8.854%	$66.3792	$66.38	$66.40	$66.40
Purchase #5	$102.29	12.827%	$115.4107	$115.41	$115.40	$115.40
Purchase #6	$145.43	6.759%	$155.2596	$155.26	$155.25	$155.30
Purchase #7	$113.95	5.229%	$119.9084	$119.91	$119.90	$119.90
7 purchase totals =	$831.48		$901.3576	$901.36	$901.35	$901.40