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	$85.65	6.170%	$90.9346	$90.93	$90.95	$90.90
Purchase #2	$41.33	11.110%	$45.9218	$45.92	$45.90	$45.90
Purchase #3	$137.89	13.471%	$156.4652	$156.47	$156.45	$156.50
Purchase #4	$62.96	6.565%	$67.0933	$67.09	$67.10	$67.10
Purchase #5	$29.34	11.433%	$32.6944	$32.69	$32.70	$32.70
Purchase #6	$15.48	11.161%	$17.2077	$17.21	$17.20	$17.20
Purchase #7	$97.63	6.213%	$103.6958	$103.70	$103.70	$103.70
7 purchase totals =	$470.28		$514.0128	$514.01	$514.00	$514.00