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	$6.78	5.121%	$7.1272	$7.13	$7.15	$7.10
Purchase #2	$25.50	8.615%	$27.6968	$27.70	$27.70	$27.70
Purchase #3	$140.51	10.681%	$155.5179	$155.52	$155.50	$155.50
Purchase #4	$231.48	10.830%	$256.5493	$256.55	$256.55	$256.50
Purchase #5	$50.52	12.671%	$56.9214	$56.92	$56.90	$56.90
Purchase #6	$139.27	8.625%	$151.282	$151.28	$151.30	$151.30
Purchase #7	$233.75	4.732%	$244.8111	$244.81	$244.80	$244.80
7 purchase totals =	$827.81		$899.9057	$899.91	$899.90	$899.80