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	$116.77	5.411%	$123.0884	$123.09	$123.10	$123.10
Purchase #2	$75.94	8.715%	$82.5582	$82.56	$82.55	$82.60
Purchase #3	$162.71	13.558%	$184.7702	$184.77	$184.75	$184.80
Purchase #4	$115.48	4.248%	$120.3856	$120.39	$120.40	$120.40
Purchase #5	$31.87	12.620%	$35.892	$35.89	$35.90	$35.90
Purchase #6	$8.83	13.516%	$10.0235	$10.02	$10.00	$10.00
Purchase #7	$105.95	6.798%	$113.1525	$113.15	$113.15	$113.20
7 purchase totals =	$617.55		$669.8704	$669.87	$669.85	$670.00