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	$79.90	7.265%	$85.7047	$85.70	$85.70	$85.70
Purchase #2	$209.29	8.575%	$227.2366	$227.24	$227.25	$227.20
Purchase #3	$103.52	5.528%	$109.2426	$109.24	$109.25	$109.20
Purchase #4	$99.82	4.810%	$104.6213	$104.62	$104.60	$104.60
Purchase #5	$150.98	13.595%	$171.5057	$171.51	$171.50	$171.50
Purchase #6	$63.71	8.107%	$68.875	$68.88	$68.90	$68.90
Purchase #7	$248.55	10.413%	$274.4315	$274.43	$274.45	$274.40
7 purchase totals =	$955.77		$1,041.6174	$1,041.62	$1,041.65	$1,041.50