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	$219.67	10.866%	$243.5393	$243.54	$243.55	$243.50
Purchase #2	$168.34	12.724%	$189.7596	$189.76	$189.75	$189.80
Purchase #3	$246.88	13.209%	$279.4904	$279.49	$279.50	$279.50
Purchase #4	$104.32	12.745%	$117.6156	$117.62	$117.60	$117.60
Purchase #5	$205.49	5.179%	$216.1323	$216.13	$216.15	$216.10
Purchase #6	$156.25	10.564%	$172.7563	$172.76	$172.75	$172.80
Purchase #7	$93.64	4.826%	$98.1591	$98.16	$98.15	$98.20
7 purchase totals =	$1,194.59		$1,317.4526	$1,317.46	$1,317.45	$1,317.50