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	$229.40	13.113%	$259.4812	$259.48	$259.50	$259.50
Purchase #2	$135.45	13.828%	$154.18	$154.18	$154.20	$154.20
Purchase #3	$126.71	12.306%	$142.3029	$142.30	$142.30	$142.30
Purchase #4	$150.62	13.705%	$171.2625	$171.26	$171.25	$171.30
Purchase #5	$149.98	4.139%	$156.1877	$156.19	$156.20	$156.20
Purchase #6	$48.60	11.402%	$54.1414	$54.14	$54.15	$54.10
Purchase #7	$59.76	6.143%	$63.4311	$63.43	$63.45	$63.40
7 purchase totals =	$900.52		$1,000.9868	$1,000.98	$1,001.05	$1,001.00