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	$83.59	9.512%	$91.5411	$91.54	$91.55	$91.50
Purchase #2	$170.69	7.215%	$183.0053	$183.01	$183.00	$183.00
Purchase #3	$85.68	9.148%	$93.518	$93.52	$93.50	$93.50
Purchase #4	$59.34	13.771%	$67.5117	$67.51	$67.50	$67.50
Purchase #5	$38.49	5.479%	$40.5989	$40.60	$40.60	$40.60
Purchase #6	$13.78	13.820%	$15.6844	$15.68	$15.70	$15.70
Purchase #7	$100.31	5.335%	$105.6615	$105.66	$105.65	$105.70
7 purchase totals =	$551.88		$597.5209	$597.52	$597.50	$597.50