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	$157.78	7.449%	$169.533	$169.53	$169.55	$169.50
Purchase #2	$128.87	9.682%	$141.3472	$141.35	$141.35	$141.30
Purchase #3	$239.51	3.639%	$248.2258	$248.23	$248.25	$248.20
Purchase #4	$54.97	10.314%	$60.6396	$60.64	$60.65	$60.60
Purchase #5	$176.51	3.569%	$182.8096	$182.81	$182.80	$182.80
Purchase #6	$177.94	12.490%	$200.1647	$200.16	$200.15	$200.20
Purchase #7	$80.74	12.284%	$90.6581	$90.66	$90.65	$90.70
7 purchase totals =	$1,016.32		$1,093.3780	$1,093.38	$1,093.40	$1,093.30