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	$43.51	9.203%	$47.5142	$47.51	$47.50	$47.50
Purchase #2	$23.81	8.271%	$25.7793	$25.78	$25.80	$25.80
Purchase #3	$140.96	11.485%	$157.1493	$157.15	$157.15	$157.10
Purchase #4	$161.49	10.538%	$178.5078	$178.51	$178.50	$178.50
Purchase #5	$102.51	12.480%	$115.3032	$115.30	$115.30	$115.30
Purchase #6	$37.60	4.632%	$39.3416	$39.34	$39.35	$39.30
Purchase #7	$35.94	4.547%	$37.5742	$37.57	$37.55	$37.60
7 purchase totals =	$545.82		$601.1696	$601.16	$601.15	$601.10