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	$139.56	12.429%	$156.9059	$156.91	$156.90	$156.90
Purchase #2	$77.74	7.190%	$83.3295	$83.33	$83.35	$83.30
Purchase #3	$66.88	5.240%	$70.3845	$70.38	$70.40	$70.40
Purchase #4	$67.77	13.311%	$76.7909	$76.79	$76.80	$76.80
Purchase #5	$186.64	6.502%	$198.7753	$198.78	$198.80	$198.80
Purchase #6	$164.51	11.581%	$183.5619	$183.56	$183.55	$183.60
Purchase #7	$49.45	4.578%	$51.7138	$51.71	$51.70	$51.70
7 purchase totals =	$752.55		$821.4618	$821.46	$821.50	$821.50