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	$37.31	4.142%	$38.8554	$38.86	$38.85	$38.90
Purchase #2	$184.98	7.769%	$199.3511	$199.35	$199.35	$199.40
Purchase #3	$161.30	4.207%	$168.0859	$168.09	$168.10	$168.10
Purchase #4	$59.75	13.412%	$67.7637	$67.76	$67.75	$67.80
Purchase #5	$134.54	4.178%	$140.1611	$140.16	$140.15	$140.20
Purchase #6	$13.31	6.171%	$14.1314	$14.13	$14.15	$14.10
Purchase #7	$37.37	11.718%	$41.749	$41.75	$41.75	$41.70
7 purchase totals =	$628.56		$670.0976	$670.10	$670.10	$670.20