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	$74.35	10.500%	$82.1568	$82.16	$82.15	$82.20
Purchase #2	$166.40	7.213%	$178.4024	$178.40	$178.40	$178.40
Purchase #3	$131.79	4.800%	$138.1159	$138.12	$138.10	$138.10
Purchase #4	$29.50	7.832%	$31.8104	$31.81	$31.80	$31.80
Purchase #5	$111.94	6.617%	$119.3471	$119.35	$119.35	$119.30
Purchase #6	$185.63	8.361%	$201.1505	$201.15	$201.15	$201.20
Purchase #7	$172.86	13.463%	$196.1321	$196.13	$196.15	$196.10
7 purchase totals =	$872.47		$947.1152	$947.12	$947.10	$947.10