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	$37.93	4.204%	$39.5246	$39.52	$39.50	$39.50
Purchase #2	$56.49	12.115%	$63.3338	$63.33	$63.35	$63.30
Purchase #3	$82.48	6.870%	$88.1464	$88.15	$88.15	$88.10
Purchase #4	$218.64	9.406%	$239.2053	$239.21	$239.20	$239.20
Purchase #5	$73.94	10.187%	$81.4723	$81.47	$81.45	$81.50
Purchase #6	$38.49	6.738%	$41.0835	$41.08	$41.10	$41.10
Purchase #7	$111.59	4.418%	$116.52	$116.52	$116.50	$116.50
7 purchase totals =	$619.56		$669.2859	$669.28	$669.25	$669.20