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	$231.76	4.205%	$241.5055	$241.51	$241.50	$241.50
Purchase #2	$95.82	4.660%	$100.2852	$100.29	$100.30	$100.30
Purchase #3	$244.54	6.106%	$259.4716	$259.47	$259.45	$259.50
Purchase #4	$151.53	8.216%	$163.9797	$163.98	$164.00	$164.00
Purchase #5	$212.47	11.429%	$236.7532	$236.75	$236.75	$236.80
Purchase #6	$71.37	12.622%	$80.3783	$80.38	$80.40	$80.40
Purchase #7	$239.46	6.873%	$255.9181	$255.92	$255.90	$255.90
7 purchase totals =	$1,246.95		$1,338.2916	$1,338.30	$1,338.30	$1,338.40