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	$40.40	7.311%	$43.3536	$43.35	$43.35	$43.40
Purchase #2	$231.75	6.384%	$246.5449	$246.54	$246.55	$246.50
Purchase #3	$59.62	11.601%	$66.5365	$66.54	$66.55	$66.50
Purchase #4	$47.48	8.819%	$51.6673	$51.67	$51.65	$51.70
Purchase #5	$62.66	7.417%	$67.3075	$67.31	$67.30	$67.30
Purchase #6	$90.39	7.573%	$97.2352	$97.24	$97.25	$97.20
Purchase #7	$18.80	9.505%	$20.5869	$20.59	$20.60	$20.60
7 purchase totals =	$551.10		$593.2319	$593.24	$593.25	$593.20