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	$74.89	3.850%	$77.7733	$77.77	$77.75	$77.80
Purchase #2	$57.35	11.221%	$63.7852	$63.79	$63.80	$63.80
Purchase #3	$143.87	3.535%	$148.9558	$148.96	$148.95	$149.00
Purchase #4	$52.66	13.495%	$59.7665	$59.77	$59.75	$59.80
Purchase #5	$203.38	11.612%	$226.9965	$227.00	$227.00	$227.00
Purchase #6	$126.78	13.698%	$144.1463	$144.15	$144.15	$144.10
Purchase #7	$35.85	5.678%	$37.8856	$37.89	$37.90	$37.90
7 purchase totals =	$694.78		$759.3092	$759.33	$759.30	$759.40