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	$103.83	7.162%	$111.2663	$111.27	$111.25	$111.30
Purchase #2	$110.79	8.215%	$119.8914	$119.89	$119.90	$119.90
Purchase #3	$77.56	5.164%	$81.5652	$81.57	$81.55	$81.60
Purchase #4	$166.49	4.633%	$174.2035	$174.20	$174.20	$174.20
Purchase #5	$223.49	13.587%	$253.8556	$253.86	$253.85	$253.90
Purchase #6	$201.31	10.541%	$222.5301	$222.53	$222.55	$222.50
Purchase #7	$159.75	10.112%	$175.9039	$175.90	$175.90	$175.90
7 purchase totals =	$1,043.22		$1,139.2160	$1,139.22	$1,139.20	$1,139.30