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	$174.39	6.371%	$185.5004	$185.50	$185.50	$185.50
Purchase #2	$198.62	11.631%	$221.7215	$221.72	$221.70	$221.70
Purchase #3	$97.25	12.430%	$109.3382	$109.34	$109.35	$109.30
Purchase #4	$119.46	10.445%	$131.9376	$131.94	$131.95	$131.90
Purchase #5	$33.85	12.294%	$38.0115	$38.01	$38.00	$38.00
Purchase #6	$42.31	7.656%	$45.5493	$45.55	$45.55	$45.50
Purchase #7	$213.26	6.761%	$227.6785	$227.68	$227.70	$227.70
7 purchase totals =	$879.14		$959.7370	$959.74	$959.75	$959.60