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	$40.49	10.403%	$44.7022	$44.70	$44.70	$44.70
Purchase #2	$85.44	8.188%	$92.4358	$92.44	$92.45	$92.40
Purchase #3	$224.75	13.858%	$255.8959	$255.90	$255.90	$255.90
Purchase #4	$98.78	6.659%	$105.3578	$105.36	$105.35	$105.40
Purchase #5	$139.27	12.700%	$156.9573	$156.96	$156.95	$157.00
Purchase #6	$103.40	10.776%	$114.5424	$114.54	$114.55	$114.50
Purchase #7	$77.82	4.617%	$81.4129	$81.41	$81.40	$81.40
7 purchase totals =	$769.95		$851.3043	$851.31	$851.30	$851.30