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	$51.38	8.390%	$55.6908	$55.69	$55.70	$55.70
Purchase #2	$117.83	9.147%	$128.6079	$128.61	$128.60	$128.60
Purchase #3	$222.66	12.472%	$250.4302	$250.43	$250.45	$250.40
Purchase #4	$218.95	8.550%	$237.6702	$237.67	$237.65	$237.70
Purchase #5	$183.97	4.230%	$191.7519	$191.75	$191.75	$191.80
Purchase #6	$142.72	3.407%	$147.5825	$147.58	$147.60	$147.60
Purchase #7	$65.90	5.449%	$69.4909	$69.49	$69.50	$69.50
7 purchase totals =	$1,003.41		$1,081.2244	$1,081.22	$1,081.25	$1,081.30