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	$35.45	9.481%	$38.811	$38.81	$38.80	$38.80
Purchase #2	$184.27	11.394%	$205.2657	$205.27	$205.25	$205.30
Purchase #3	$55.80	12.192%	$62.6031	$62.60	$62.60	$62.60
Purchase #4	$30.91	11.840%	$34.5697	$34.57	$34.55	$34.60
Purchase #5	$6.87	13.180%	$7.7755	$7.78	$7.80	$7.80
Purchase #6	$35.72	6.116%	$37.9046	$37.90	$37.90	$37.90
Purchase #7	$186.90	11.484%	$208.3636	$208.36	$208.35	$208.40
7 purchase totals =	$535.92		$595.2932	$595.29	$595.25	$595.40