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	$158.88	12.425%	$178.6208	$178.62	$178.60	$178.60
Purchase #2	$249.44	13.469%	$283.0371	$283.04	$283.05	$283.00
Purchase #3	$57.99	7.656%	$62.4297	$62.43	$62.45	$62.40
Purchase #4	$69.27	9.592%	$75.9144	$75.91	$75.90	$75.90
Purchase #5	$55.48	7.275%	$59.5162	$59.52	$59.50	$59.50
Purchase #6	$77.81	6.628%	$82.9672	$82.97	$82.95	$83.00
Purchase #7	$83.87	6.247%	$89.1094	$89.11	$89.10	$89.10
7 purchase totals =	$752.74		$831.5948	$831.60	$831.55	$831.50