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	$92.96	6.387%	$98.8974	$98.90	$98.90	$98.90
Purchase #2	$95.58	10.325%	$105.4486	$105.45	$105.45	$105.40
Purchase #3	$79.48	12.811%	$89.6622	$89.66	$89.65	$89.70
Purchase #4	$94.47	11.481%	$105.3161	$105.32	$105.30	$105.30
Purchase #5	$131.58	5.115%	$138.3103	$138.31	$138.30	$138.30
Purchase #6	$52.79	10.434%	$58.2981	$58.30	$58.30	$58.30
Purchase #7	$167.77	12.832%	$189.2982	$189.30	$189.30	$189.30
7 purchase totals =	$714.63		$785.2309	$785.24	$785.20	$785.20