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	$46.33	13.423%	$52.5489	$52.55	$52.55	$52.50
Purchase #2	$20.98	12.214%	$23.5425	$23.54	$23.55	$23.50
Purchase #3	$131.34	13.235%	$148.7228	$148.72	$148.70	$148.70
Purchase #4	$99.95	10.789%	$110.7336	$110.73	$110.75	$110.70
Purchase #5	$49.79	13.544%	$56.5336	$56.53	$56.55	$56.50
Purchase #6	$101.86	9.415%	$111.4501	$111.45	$111.45	$111.50
Purchase #7	$176.73	5.390%	$186.2557	$186.26	$186.25	$186.30
7 purchase totals =	$626.98		$689.7872	$689.78	$689.80	$689.70