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	$55.57	7.468%	$59.72	$59.72	$59.70	$59.70
Purchase #2	$86.43	4.274%	$90.124	$90.12	$90.10	$90.10
Purchase #3	$140.91	13.493%	$159.923	$159.92	$159.90	$159.90
Purchase #4	$109.89	12.499%	$123.6252	$123.63	$123.65	$123.60
Purchase #5	$158.36	12.617%	$178.3403	$178.34	$178.35	$178.30
Purchase #6	$103.55	10.837%	$114.7717	$114.77	$114.75	$114.80
Purchase #7	$131.65	9.537%	$144.2055	$144.21	$144.20	$144.20
7 purchase totals =	$786.36		$870.7097	$870.71	$870.65	$870.60