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	$53.63	4.579%	$56.0857	$56.09	$56.10	$56.10
Purchase #2	$89.26	12.516%	$100.4318	$100.43	$100.45	$100.40
Purchase #3	$42.30	13.550%	$48.0317	$48.03	$48.05	$48.00
Purchase #4	$36.87	8.561%	$40.0264	$40.03	$40.05	$40.00
Purchase #5	$31.89	3.211%	$32.914	$32.91	$32.90	$32.90
Purchase #6	$7.85	5.169%	$8.2558	$8.26	$8.25	$8.30
Purchase #7	$165.85	9.537%	$181.6671	$181.67	$181.65	$181.70
7 purchase totals =	$427.65		$467.4125	$467.42	$467.45	$467.40