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	$214.83	11.365%	$239.2454	$239.25	$239.25	$239.20
Purchase #2	$178.56	12.339%	$200.5925	$200.59	$200.60	$200.60
Purchase #3	$86.83	13.800%	$98.8125	$98.81	$98.80	$98.80
Purchase #4	$88.32	12.452%	$99.3176	$99.32	$99.30	$99.30
Purchase #5	$128.72	9.545%	$141.0063	$141.01	$141.00	$141.00
Purchase #6	$128.96	7.512%	$138.6475	$138.65	$138.65	$138.60
Purchase #7	$138.86	12.872%	$156.7341	$156.73	$156.75	$156.70
7 purchase totals =	$965.08		$1,074.3559	$1,074.36	$1,074.35	$1,074.20