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	$75.85	3.577%	$78.5632	$78.56	$78.55	$78.60
Purchase #2	$76.58	13.356%	$86.808	$86.81	$86.80	$86.80
Purchase #3	$225.64	10.390%	$249.084	$249.08	$249.10	$249.10
Purchase #4	$97.32	8.499%	$105.5912	$105.59	$105.60	$105.60
Purchase #5	$110.85	9.399%	$121.2688	$121.27	$121.25	$121.30
Purchase #6	$128.49	13.312%	$145.5946	$145.59	$145.60	$145.60
Purchase #7	$194.63	8.214%	$210.6169	$210.62	$210.60	$210.60
7 purchase totals =	$909.36		$997.5267	$997.52	$997.50	$997.60