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	$225.36	13.654%	$256.1307	$256.13	$256.15	$256.10
Purchase #2	$140.72	11.536%	$156.9535	$156.95	$156.95	$157.00
Purchase #3	$170.73	10.856%	$189.2644	$189.26	$189.25	$189.30
Purchase #4	$24.84	12.790%	$28.017	$28.02	$28.00	$28.00
Purchase #5	$156.76	9.459%	$171.5879	$171.59	$171.60	$171.60
Purchase #6	$151.74	3.800%	$157.5061	$157.51	$157.50	$157.50
Purchase #7	$68.77	4.590%	$71.9265	$71.93	$71.95	$71.90
7 purchase totals =	$938.92		$1,031.3861	$1,031.39	$1,031.40	$1,031.40