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	$92.90	6.808%	$99.2246	$99.22	$99.20	$99.20
Purchase #2	$37.36	8.874%	$40.6753	$40.68	$40.70	$40.70
Purchase #3	$145.42	4.185%	$151.5058	$151.51	$151.50	$151.50
Purchase #4	$124.65	5.770%	$131.8423	$131.84	$131.85	$131.80
Purchase #5	$72.59	8.404%	$78.6905	$78.69	$78.70	$78.70
Purchase #6	$20.79	12.374%	$23.3626	$23.36	$23.35	$23.40
Purchase #7	$38.71	4.815%	$40.5739	$40.57	$40.55	$40.60
7 purchase totals =	$532.42		$565.8750	$565.87	$565.85	$565.90