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	$89.42	12.801%	$100.8667	$100.87	$100.85	$100.90
Purchase #2	$40.50	12.409%	$45.5256	$45.53	$45.55	$45.50
Purchase #3	$16.86	6.631%	$17.978	$17.98	$18.00	$18.00
Purchase #4	$223.48	11.176%	$248.4561	$248.46	$248.45	$248.50
Purchase #5	$134.65	6.167%	$142.9539	$142.95	$142.95	$143.00
Purchase #6	$188.84	6.142%	$200.4386	$200.44	$200.45	$200.40
Purchase #7	$14.84	12.108%	$16.6368	$16.64	$16.65	$16.60
7 purchase totals =	$708.59		$772.8557	$772.87	$772.90	$772.90