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	$100.54	9.840%	$110.4331	$110.43	$110.45	$110.40
Purchase #2	$64.47	9.830%	$70.8074	$70.81	$70.80	$70.80
Purchase #3	$38.31	10.847%	$42.4655	$42.47	$42.45	$42.50
Purchase #4	$204.61	8.665%	$222.3395	$222.34	$222.35	$222.30
Purchase #5	$189.67	4.632%	$198.4555	$198.46	$198.45	$198.50
Purchase #6	$40.45	11.813%	$45.2284	$45.23	$45.25	$45.20
Purchase #7	$74.93	9.304%	$81.9015	$81.90	$81.90	$81.90
7 purchase totals =	$712.98		$771.6309	$771.64	$771.65	$771.60