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	$52.40	13.303%	$59.3708	$59.37	$59.35	$59.40
Purchase #2	$106.93	10.141%	$117.7738	$117.77	$117.75	$117.80
Purchase #3	$49.54	9.408%	$54.2007	$54.20	$54.20	$54.20
Purchase #4	$108.48	4.545%	$113.4104	$113.41	$113.40	$113.40
Purchase #5	$218.55	10.122%	$240.6716	$240.67	$240.65	$240.70
Purchase #6	$116.34	9.301%	$127.1608	$127.16	$127.15	$127.20
Purchase #7	$180.80	12.449%	$203.3078	$203.31	$203.30	$203.30
7 purchase totals =	$833.04		$915.8959	$915.89	$915.80	$916.00