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	$71.58	9.738%	$78.5505	$78.55	$78.55	$78.60
Purchase #2	$49.85	5.309%	$52.4965	$52.50	$52.50	$52.50
Purchase #3	$47.58	12.242%	$53.4047	$53.40	$53.40	$53.40
Purchase #4	$128.55	4.216%	$133.9697	$133.97	$133.95	$134.00
Purchase #5	$37.67	3.786%	$39.0962	$39.10	$39.10	$39.10
Purchase #6	$173.50	13.400%	$196.749	$196.75	$196.75	$196.70
Purchase #7	$234.78	9.758%	$257.6898	$257.69	$257.70	$257.70
7 purchase totals =	$743.51		$811.9564	$811.96	$811.95	$812.00