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	$26.81	11.177%	$29.8066	$29.81	$29.80	$29.80
Purchase #2	$174.97	12.373%	$196.619	$196.62	$196.60	$196.60
Purchase #3	$63.91	13.553%	$72.5717	$72.57	$72.55	$72.60
Purchase #4	$221.48	8.197%	$239.6347	$239.63	$239.65	$239.60
Purchase #5	$238.80	4.277%	$249.0135	$249.01	$249.00	$249.00
Purchase #6	$99.93	11.660%	$111.5818	$111.58	$111.60	$111.60
Purchase #7	$6.64	9.163%	$7.2484	$7.25	$7.25	$7.20
7 purchase totals =	$832.54		$906.4757	$906.47	$906.45	$906.40