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	$10.87	11.243%	$12.0921	$12.09	$12.10	$12.10
Purchase #2	$149.48	5.874%	$158.2605	$158.26	$158.25	$158.30
Purchase #3	$142.78	5.138%	$150.116	$150.12	$150.10	$150.10
Purchase #4	$208.38	13.520%	$236.553	$236.55	$236.55	$236.60
Purchase #5	$49.46	3.769%	$51.3241	$51.32	$51.30	$51.30
Purchase #6	$220.78	13.648%	$250.9121	$250.91	$250.90	$250.90
Purchase #7	$39.99	6.364%	$42.535	$42.54	$42.55	$42.50
7 purchase totals =	$821.74		$901.7928	$901.79	$901.75	$901.80