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	$57.52	11.337%	$64.041	$64.04	$64.05	$64.00
Purchase #2	$183.96	8.566%	$199.718	$199.72	$199.70	$199.70
Purchase #3	$136.50	13.465%	$154.8797	$154.88	$154.90	$154.90
Purchase #4	$37.62	13.794%	$42.8093	$42.81	$42.80	$42.80
Purchase #5	$176.32	6.394%	$187.5939	$187.59	$187.60	$187.60
Purchase #6	$246.58	13.825%	$280.6697	$280.67	$280.65	$280.70
Purchase #7	$82.91	3.505%	$85.816	$85.82	$85.80	$85.80
7 purchase totals =	$921.41		$1,015.5276	$1,015.53	$1,015.50	$1,015.50