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	$46.43	13.268%	$52.5903	$52.59	$52.60	$52.60
Purchase #2	$85.93	4.575%	$89.8613	$89.86	$89.85	$89.90
Purchase #3	$212.54	5.585%	$224.4104	$224.41	$224.40	$224.40
Purchase #4	$121.81	8.554%	$132.2296	$132.23	$132.25	$132.20
Purchase #5	$33.66	4.282%	$35.1013	$35.10	$35.10	$35.10
Purchase #6	$156.68	13.800%	$178.3018	$178.30	$178.30	$178.30
Purchase #7	$58.44	12.148%	$65.5393	$65.54	$65.55	$65.50
7 purchase totals =	$715.49		$778.0340	$778.03	$778.05	$778.00