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	$118.35	8.359%	$128.2429	$128.24	$128.25	$128.20
Purchase #2	$129.75	12.646%	$146.1582	$146.16	$146.15	$146.20
Purchase #3	$201.61	8.368%	$218.4807	$218.48	$218.50	$218.50
Purchase #4	$131.81	9.767%	$144.6839	$144.68	$144.70	$144.70
Purchase #5	$152.85	9.181%	$166.8832	$166.88	$166.90	$166.90
Purchase #6	$148.55	5.423%	$156.6059	$156.61	$156.60	$156.60
Purchase #7	$139.98	11.727%	$156.3955	$156.40	$156.40	$156.40
7 purchase totals =	$1,022.90		$1,117.4503	$1,117.45	$1,117.50	$1,117.50