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	$70.48	10.776%	$78.0749	$78.07	$78.05	$78.10
Purchase #2	$101.88	11.827%	$113.9293	$113.93	$113.95	$113.90
Purchase #3	$41.59	5.235%	$43.7672	$43.77	$43.75	$43.80
Purchase #4	$64.77	6.697%	$69.1076	$69.11	$69.10	$69.10
Purchase #5	$124.65	9.682%	$136.7186	$136.72	$136.70	$136.70
Purchase #6	$227.39	13.868%	$258.9244	$258.92	$258.90	$258.90
Purchase #7	$134.30	3.549%	$139.0663	$139.07	$139.05	$139.10
7 purchase totals =	$765.06		$839.5883	$839.59	$839.50	$839.60