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	$81.67	9.178%	$89.1657	$89.17	$89.15	$89.20
Purchase #2	$140.89	8.520%	$152.8938	$152.89	$152.90	$152.90
Purchase #3	$8.90	6.836%	$9.5084	$9.51	$9.50	$9.50
Purchase #4	$50.70	6.573%	$54.0325	$54.03	$54.05	$54.00
Purchase #5	$60.55	11.517%	$67.5235	$67.52	$67.50	$67.50
Purchase #6	$176.68	5.779%	$186.8903	$186.89	$186.90	$186.90
Purchase #7	$41.77	5.836%	$44.2077	$44.21	$44.20	$44.20
7 purchase totals =	$561.16		$604.2219	$604.22	$604.20	$604.20