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	$11.31	10.552%	$12.5034	$12.50	$12.50	$12.50
Purchase #2	$162.65	5.813%	$172.1048	$172.10	$172.10	$172.10
Purchase #3	$31.28	11.646%	$34.9229	$34.92	$34.90	$34.90
Purchase #4	$196.79	8.699%	$213.9088	$213.91	$213.90	$213.90
Purchase #5	$38.36	8.215%	$41.5113	$41.51	$41.50	$41.50
Purchase #6	$91.63	9.460%	$100.2982	$100.30	$100.30	$100.30
Purchase #7	$115.70	7.282%	$124.1253	$124.13	$124.15	$124.10
7 purchase totals =	$647.72		$699.3747	$699.37	$699.35	$699.30