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	$108.52	7.514%	$116.6742	$116.67	$116.65	$116.70
Purchase #2	$25.72	6.684%	$27.4391	$27.44	$27.45	$27.40
Purchase #3	$239.43	10.462%	$264.4792	$264.48	$264.50	$264.50
Purchase #4	$229.54	13.479%	$260.4797	$260.48	$260.50	$260.50
Purchase #5	$87.88	9.314%	$96.0651	$96.07	$96.05	$96.10
Purchase #6	$76.80	8.492%	$83.3219	$83.32	$83.30	$83.30
Purchase #7	$130.83	9.743%	$143.5768	$143.58	$143.60	$143.60
7 purchase totals =	$898.72		$992.0360	$992.04	$992.05	$992.10