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	$22.94	8.250%	$24.8326	$24.83	$24.85	$24.80
Purchase #2	$104.75	11.248%	$116.5323	$116.53	$116.55	$116.50
Purchase #3	$9.89	8.370%	$10.7178	$10.72	$10.70	$10.70
Purchase #4	$239.52	3.517%	$247.9439	$247.94	$247.95	$247.90
Purchase #5	$175.96	10.482%	$194.4041	$194.40	$194.40	$194.40
Purchase #6	$182.91	7.542%	$196.7051	$196.71	$196.70	$196.70
Purchase #7	$84.37	6.409%	$89.7773	$89.78	$89.80	$89.80
7 purchase totals =	$820.34		$880.9131	$880.91	$880.95	$880.80