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	$250.53	3.168%	$258.4668	$258.47	$258.45	$258.50
Purchase #2	$71.81	12.564%	$80.8322	$80.83	$80.85	$80.80
Purchase #3	$34.91	7.604%	$37.5646	$37.56	$37.55	$37.60
Purchase #4	$229.35	13.286%	$259.8214	$259.82	$259.80	$259.80
Purchase #5	$148.90	10.280%	$164.2069	$164.21	$164.20	$164.20
Purchase #6	$240.27	7.635%	$258.6146	$258.61	$258.60	$258.60
Purchase #7	$13.34	5.498%	$14.0734	$14.07	$14.05	$14.10
7 purchase totals =	$989.11		$1,073.5799	$1,073.57	$1,073.50	$1,073.60