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	$203.99	6.564%	$217.3799	$217.38	$217.40	$217.40
Purchase #2	$179.88	11.426%	$200.4331	$200.43	$200.45	$200.40
Purchase #3	$134.57	11.184%	$149.6203	$149.62	$149.60	$149.60
Purchase #4	$45.64	4.134%	$47.5268	$47.53	$47.55	$47.50
Purchase #5	$208.82	12.330%	$234.5675	$234.57	$234.55	$234.60
Purchase #6	$38.91	12.784%	$43.8843	$43.88	$43.90	$43.90
Purchase #7	$130.61	7.534%	$140.4502	$140.45	$140.45	$140.50
7 purchase totals =	$942.42		$1,033.8621	$1,033.86	$1,033.90	$1,033.90