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	$222.28	12.869%	$250.8852	$250.89	$250.90	$250.90
Purchase #2	$136.32	8.487%	$147.8895	$147.89	$147.90	$147.90
Purchase #3	$21.72	5.752%	$22.9693	$22.97	$22.95	$23.00
Purchase #4	$52.72	3.182%	$54.3976	$54.40	$54.40	$54.40
Purchase #5	$51.64	9.188%	$56.3847	$56.38	$56.40	$56.40
Purchase #6	$80.95	10.696%	$89.6084	$89.61	$89.60	$89.60
Purchase #7	$194.96	4.311%	$203.3647	$203.36	$203.35	$203.40
7 purchase totals =	$760.59		$825.4994	$825.50	$825.50	$825.60