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	$37.61	4.673%	$39.3675	$39.37	$39.35	$39.40
Purchase #2	$76.94	7.628%	$82.809	$82.81	$82.80	$82.80
Purchase #3	$133.59	12.531%	$150.3302	$150.33	$150.35	$150.30
Purchase #4	$228.71	12.755%	$257.882	$257.88	$257.90	$257.90
Purchase #5	$56.90	8.498%	$61.7354	$61.74	$61.75	$61.70
Purchase #6	$174.47	10.208%	$192.2799	$192.28	$192.30	$192.30
Purchase #7	$219.87	12.153%	$246.5908	$246.59	$246.60	$246.60
7 purchase totals =	$928.09		$1,030.9948	$1,031.00	$1,031.05	$1,031.00