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	$74.45	12.715%	$83.9163	$83.92	$83.90	$83.90
Purchase #2	$206.55	12.214%	$231.778	$231.78	$231.80	$231.80
Purchase #3	$72.44	9.687%	$79.4573	$79.46	$79.45	$79.50
Purchase #4	$221.96	10.734%	$245.7852	$245.79	$245.80	$245.80
Purchase #5	$11.57	8.720%	$12.5789	$12.58	$12.60	$12.60
Purchase #6	$228.64	5.340%	$240.8494	$240.85	$240.85	$240.80
Purchase #7	$134.88	7.422%	$144.8908	$144.89	$144.90	$144.90
7 purchase totals =	$950.49		$1,039.2559	$1,039.27	$1,039.30	$1,039.30