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	$131.66	4.847%	$138.0416	$138.04	$138.05	$138.00
Purchase #2	$100.97	4.796%	$105.8125	$105.81	$105.80	$105.80
Purchase #3	$173.51	5.448%	$182.9628	$182.96	$182.95	$183.00
Purchase #4	$136.46	3.132%	$140.7339	$140.73	$140.75	$140.70
Purchase #5	$148.45	12.357%	$166.794	$166.79	$166.80	$166.80
Purchase #6	$38.37	5.526%	$40.4903	$40.49	$40.50	$40.50
Purchase #7	$190.50	5.285%	$200.5679	$200.57	$200.55	$200.60
7 purchase totals =	$919.92		$975.4030	$975.39	$975.40	$975.40