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	$229.76	11.867%	$257.0256	$257.03	$257.05	$257.00
Purchase #2	$40.93	10.656%	$45.2915	$45.29	$45.30	$45.30
Purchase #3	$20.33	7.630%	$21.8812	$21.88	$21.90	$21.90
Purchase #4	$174.82	9.813%	$191.9751	$191.98	$192.00	$192.00
Purchase #5	$224.50	12.839%	$253.3236	$253.32	$253.30	$253.30
Purchase #6	$116.81	9.401%	$127.7913	$127.79	$127.80	$127.80
Purchase #7	$65.43	6.328%	$69.5704	$69.57	$69.55	$69.60
7 purchase totals =	$872.58		$966.8587	$966.86	$966.90	$966.90