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	$17.30	6.187%	$18.3704	$18.37	$18.35	$18.40
Purchase #2	$90.75	7.411%	$97.4755	$97.48	$97.50	$97.50
Purchase #3	$59.37	5.125%	$62.4127	$62.41	$62.40	$62.40
Purchase #4	$196.29	9.841%	$215.6069	$215.61	$215.60	$215.60
Purchase #5	$206.47	10.586%	$228.3269	$228.33	$228.35	$228.30
Purchase #6	$66.55	10.268%	$73.3834	$73.38	$73.40	$73.40
Purchase #7	$63.83	5.145%	$67.1141	$67.11	$67.10	$67.10
7 purchase totals =	$700.56		$762.6899	$762.69	$762.70	$762.70