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	$27.82	12.757%	$31.369	$31.37	$31.35	$31.40
Purchase #2	$114.42	4.114%	$119.1272	$119.13	$119.15	$119.10
Purchase #3	$73.65	12.161%	$82.6066	$82.61	$82.60	$82.60
Purchase #4	$73.88	9.859%	$81.1638	$81.16	$81.15	$81.20
Purchase #5	$40.30	7.272%	$43.2306	$43.23	$43.25	$43.20
Purchase #6	$73.91	10.503%	$81.6728	$81.67	$81.65	$81.70
Purchase #7	$145.92	10.543%	$161.3043	$161.30	$161.30	$161.30
7 purchase totals =	$549.90		$600.4743	$600.47	$600.45	$600.50