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	$114.53	3.230%	$118.2293	$118.23	$118.25	$118.20
Purchase #2	$78.49	3.814%	$81.4836	$81.48	$81.50	$81.50
Purchase #3	$250.58	12.630%	$282.2283	$282.23	$282.25	$282.20
Purchase #4	$38.75	5.517%	$40.8878	$40.89	$40.90	$40.90
Purchase #5	$112.79	4.453%	$117.8125	$117.81	$117.80	$117.80
Purchase #6	$120.97	5.460%	$127.575	$127.58	$127.60	$127.60
Purchase #7	$13.71	8.523%	$14.8785	$14.88	$14.90	$14.90
7 purchase totals =	$729.82		$783.0950	$783.10	$783.20	$783.10