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	$14.56	6.339%	$15.483	$15.48	$15.50	$15.50
Purchase #2	$203.82	3.608%	$211.1738	$211.17	$211.15	$211.20
Purchase #3	$238.61	11.504%	$266.0597	$266.06	$266.05	$266.10
Purchase #4	$69.62	13.258%	$78.8502	$78.85	$78.85	$78.90
Purchase #5	$41.44	12.807%	$46.7472	$46.75	$46.75	$46.70
Purchase #6	$150.33	8.387%	$162.9382	$162.94	$162.95	$162.90
Purchase #7	$81.78	4.736%	$85.6531	$85.65	$85.65	$85.70
7 purchase totals =	$800.16		$866.9052	$866.90	$866.90	$867.00