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	$78.72	3.501%	$81.476	$81.48	$81.50	$81.50
Purchase #2	$29.54	5.836%	$31.264	$31.26	$31.25	$31.30
Purchase #3	$250.39	5.181%	$263.3627	$263.36	$263.35	$263.40
Purchase #4	$37.45	12.645%	$42.1856	$42.19	$42.20	$42.20
Purchase #5	$195.97	9.414%	$214.4186	$214.42	$214.40	$214.40
Purchase #6	$108.33	13.696%	$123.1669	$123.17	$123.15	$123.20
Purchase #7	$37.28	8.267%	$40.3619	$40.36	$40.35	$40.40
7 purchase totals =	$737.68		$796.2357	$796.24	$796.20	$796.40