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	$139.56	11.786%	$156.0085	$156.01	$156.00	$156.00
Purchase #2	$53.59	7.332%	$57.5192	$57.52	$57.50	$57.50
Purchase #3	$63.51	11.226%	$70.6396	$70.64	$70.65	$70.60
Purchase #4	$196.55	13.591%	$223.2631	$223.26	$223.25	$223.30
Purchase #5	$119.93	12.314%	$134.6982	$134.70	$134.70	$134.70
Purchase #6	$31.98	11.651%	$35.706	$35.71	$35.70	$35.70
Purchase #7	$79.87	12.507%	$89.8593	$89.86	$89.85	$89.90
7 purchase totals =	$684.99		$767.6939	$767.70	$767.65	$767.70