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	$37.48	7.581%	$40.3214	$40.32	$40.30	$40.30
Purchase #2	$123.94	5.705%	$131.0108	$131.01	$131.00	$131.00
Purchase #3	$9.77	12.792%	$11.0198	$11.02	$11.00	$11.00
Purchase #4	$11.53	6.682%	$12.3004	$12.30	$12.30	$12.30
Purchase #5	$42.80	9.574%	$46.8977	$46.90	$46.90	$46.90
Purchase #6	$135.67	3.102%	$139.8785	$139.88	$139.90	$139.90
Purchase #7	$46.32	10.222%	$51.0548	$51.05	$51.05	$51.10
7 purchase totals =	$407.51		$432.4834	$432.48	$432.45	$432.50