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	$81.89	5.640%	$86.5086	$86.51	$86.50	$86.50
Purchase #2	$228.92	11.614%	$255.5068	$255.51	$255.50	$255.50
Purchase #3	$164.54	9.570%	$180.2865	$180.29	$180.30	$180.30
Purchase #4	$171.63	13.773%	$195.2686	$195.27	$195.25	$195.30
Purchase #5	$143.93	13.439%	$163.2728	$163.27	$163.25	$163.30
Purchase #6	$209.75	8.474%	$227.5242	$227.52	$227.50	$227.50
Purchase #7	$103.70	8.807%	$112.8329	$112.83	$112.85	$112.80
7 purchase totals =	$1,104.36		$1,221.2004	$1,221.20	$1,221.15	$1,221.20