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	$142.65	9.587%	$156.3259	$156.33	$156.35	$156.30
Purchase #2	$235.32	4.847%	$246.726	$246.73	$246.75	$246.70
Purchase #3	$31.53	7.498%	$33.8941	$33.89	$33.90	$33.90
Purchase #4	$46.59	3.645%	$48.2882	$48.29	$48.30	$48.30
Purchase #5	$51.45	4.582%	$53.8074	$53.81	$53.80	$53.80
Purchase #6	$11.52	10.236%	$12.6992	$12.70	$12.70	$12.70
Purchase #7	$78.72	11.392%	$87.6878	$87.69	$87.70	$87.70
7 purchase totals =	$597.78		$639.4286	$639.44	$639.50	$639.40