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	$176.44	5.205%	$185.6237	$185.62	$185.60	$185.60
Purchase #2	$225.88	4.197%	$235.3602	$235.36	$235.35	$235.40
Purchase #3	$112.30	13.562%	$127.5301	$127.53	$127.55	$127.50
Purchase #4	$53.79	8.231%	$58.2175	$58.22	$58.20	$58.20
Purchase #5	$30.59	4.143%	$31.8573	$31.86	$31.85	$31.90
Purchase #6	$89.38	12.473%	$100.5284	$100.53	$100.55	$100.50
Purchase #7	$151.43	6.835%	$161.7802	$161.78	$161.80	$161.80
7 purchase totals =	$839.81		$900.8974	$900.90	$900.90	$900.90