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	$106.70	9.305%	$116.6284	$116.63	$116.65	$116.60
Purchase #2	$191.61	11.461%	$213.5704	$213.57	$213.55	$213.60
Purchase #3	$41.34	5.784%	$43.7311	$43.73	$43.75	$43.70
Purchase #4	$49.58	4.483%	$51.8027	$51.80	$51.80	$51.80
Purchase #5	$30.25	7.297%	$32.4573	$32.46	$32.45	$32.50
Purchase #6	$115.97	11.160%	$128.9123	$128.91	$128.90	$128.90
Purchase #7	$54.34	9.330%	$59.4099	$59.41	$59.40	$59.40
7 purchase totals =	$589.79		$646.5121	$646.51	$646.50	$646.50