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	$139.40	10.568%	$154.1318	$154.13	$154.15	$154.10
Purchase #2	$245.91	4.346%	$256.5972	$256.60	$256.60	$256.60
Purchase #3	$59.69	9.252%	$65.2125	$65.21	$65.20	$65.20
Purchase #4	$136.55	13.739%	$155.3106	$155.31	$155.30	$155.30
Purchase #5	$102.44	13.850%	$116.6279	$116.63	$116.65	$116.60
Purchase #6	$56.77	8.463%	$61.5744	$61.57	$61.55	$61.60
Purchase #7	$101.25	8.158%	$109.51	$109.51	$109.50	$109.50
7 purchase totals =	$842.01		$918.9644	$918.96	$918.95	$918.90