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	$37.47	7.771%	$40.3818	$40.38	$40.40	$40.40
Purchase #2	$102.67	12.527%	$115.5315	$115.53	$115.55	$115.50
Purchase #3	$17.39	7.599%	$18.7115	$18.71	$18.70	$18.70
Purchase #4	$63.69	6.552%	$67.863	$67.86	$67.85	$67.90
Purchase #5	$5.65	4.641%	$5.9122	$5.91	$5.90	$5.90
Purchase #6	$32.53	8.776%	$35.3848	$35.38	$35.40	$35.40
Purchase #7	$238.85	13.687%	$271.5414	$271.54	$271.55	$271.50
7 purchase totals =	$498.25		$555.3262	$555.31	$555.35	$555.30