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	$35.29	13.778%	$40.1523	$40.15	$40.15	$40.20
Purchase #2	$250.76	12.331%	$281.6812	$281.68	$281.70	$281.70
Purchase #3	$36.89	4.491%	$38.5467	$38.55	$38.55	$38.50
Purchase #4	$85.91	6.451%	$91.4521	$91.45	$91.45	$91.50
Purchase #5	$141.87	12.497%	$159.5995	$159.60	$159.60	$159.60
Purchase #6	$208.58	9.529%	$228.4556	$228.46	$228.45	$228.50
Purchase #7	$245.90	10.855%	$272.5924	$272.59	$272.60	$272.60
7 purchase totals =	$1,005.20		$1,112.4798	$1,112.48	$1,112.50	$1,112.60