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	$12.86	6.789%	$13.7331	$13.73	$13.75	$13.70
Purchase #2	$99.31	5.310%	$104.5834	$104.58	$104.60	$104.60
Purchase #3	$113.97	3.595%	$118.0672	$118.07	$118.05	$118.10
Purchase #4	$186.26	5.250%	$196.0387	$196.04	$196.05	$196.00
Purchase #5	$54.38	9.216%	$59.3917	$59.39	$59.40	$59.40
Purchase #6	$104.42	5.780%	$110.4555	$110.46	$110.45	$110.50
Purchase #7	$12.87	12.844%	$14.523	$14.52	$14.50	$14.50
7 purchase totals =	$584.07		$616.7926	$616.79	$616.80	$616.80