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	$20.38	9.712%	$22.3593	$22.36	$22.35	$22.40
Purchase #2	$40.79	4.276%	$42.5342	$42.53	$42.55	$42.50
Purchase #3	$228.90	9.161%	$249.8695	$249.87	$249.85	$249.90
Purchase #4	$56.78	5.363%	$59.8251	$59.83	$59.85	$59.80
Purchase #5	$116.71	12.208%	$130.958	$130.96	$130.95	$131.00
Purchase #6	$231.78	3.440%	$239.7532	$239.75	$239.75	$239.80
Purchase #7	$140.52	6.452%	$149.5864	$149.59	$149.60	$149.60
7 purchase totals =	$835.86		$894.8857	$894.89	$894.90	$895.00