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	$154.80	10.627%	$171.2506	$171.25	$171.25	$171.30
Purchase #2	$130.64	5.264%	$137.5169	$137.52	$137.50	$137.50
Purchase #3	$35.47	13.383%	$40.217	$40.22	$40.20	$40.20
Purchase #4	$8.92	8.807%	$9.7056	$9.71	$9.70	$9.70
Purchase #5	$181.60	12.391%	$204.1021	$204.10	$204.10	$204.10
Purchase #6	$85.30	5.348%	$89.8618	$89.86	$89.85	$89.90
Purchase #7	$78.96	8.821%	$85.9251	$85.93	$85.95	$85.90
7 purchase totals =	$675.69		$738.5791	$738.59	$738.55	$738.60