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	$11.27	5.394%	$11.8779	$11.88	$11.90	$11.90
Purchase #2	$107.79	3.708%	$111.7869	$111.79	$111.80	$111.80
Purchase #3	$227.73	4.374%	$237.6909	$237.69	$237.70	$237.70
Purchase #4	$99.97	4.156%	$104.1248	$104.12	$104.10	$104.10
Purchase #5	$91.54	10.340%	$101.0052	$101.01	$101.00	$101.00
Purchase #6	$213.31	8.660%	$231.7826	$231.78	$231.80	$231.80
Purchase #7	$20.48	4.178%	$21.3357	$21.34	$21.35	$21.30
7 purchase totals =	$772.09		$819.6040	$819.61	$819.65	$819.60