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	$17.72	3.117%	$18.2723	$18.27	$18.25	$18.30
Purchase #2	$78.98	12.737%	$89.0397	$89.04	$89.05	$89.00
Purchase #3	$29.97	4.194%	$31.2269	$31.23	$31.25	$31.20
Purchase #4	$168.66	11.105%	$187.3897	$187.39	$187.40	$187.40
Purchase #5	$119.53	7.632%	$128.6525	$128.65	$128.65	$128.70
Purchase #6	$153.97	11.289%	$171.3517	$171.35	$171.35	$171.40
Purchase #7	$186.60	3.641%	$193.3941	$193.39	$193.40	$193.40
7 purchase totals =	$755.43		$819.3269	$819.32	$819.35	$819.40